crypto: qat - Avoid -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
ready to enable it globally.

Use the `__struct_group()` helper to separate the flexible array
from the rest of the members in flexible `struct qat_alg_buf_list`,
through tagged `struct qat_alg_buf_list_hdr`, and avoid embedding the
flexible-array member in the middle of `struct qat_alg_fixed_buf_list`.

Also, use `container_of()` whenever we need to retrieve a pointer to
the flexible structure.

So, with these changes, fix the following warnings:
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/crypto/intel/qat/qat_common/qat_bl.h:25:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: https://github.com/KSPP/linux/issues/202
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Acked-by: Giovanni Cabiddu <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/crypto/intel/qat/qat_common/qat_bl.c

···
 		if (unlikely(!bufl))
 			return -ENOMEM;
 	} else {
-		bufl = &buf->sgl_src.sgl_hdr;
+		bufl = container_of(&buf->sgl_src.sgl_hdr,
+				    struct qat_alg_buf_list, hdr);
 		memset(bufl, 0, sizeof(struct qat_alg_buf_list));
 		buf->sgl_src_valid = true;
 	}
···
 			if (unlikely(!buflout))
 				goto err_in;
 		} else {
-			buflout = &buf->sgl_dst.sgl_hdr;
+			buflout = container_of(&buf->sgl_dst.sgl_hdr,
+					       struct qat_alg_buf_list, hdr);
 			memset(buflout, 0, sizeof(struct qat_alg_buf_list));
 			buf->sgl_dst_valid = true;
 		}

drivers/crypto/intel/qat/qat_common/qat_bl.h

···
 } __packed;
 
 struct qat_alg_buf_list {
-	u64 resrvd;
-	u32 num_bufs;
-	u32 num_mapped_bufs;
+	/* New members must be added within the __struct_group() macro below. */
+	__struct_group(qat_alg_buf_list_hdr, hdr, __packed,
+		u64 resrvd;
+		u32 num_bufs;
+		u32 num_mapped_bufs;
+	);
 	struct qat_alg_buf buffers[];
 } __packed;
 
 struct qat_alg_fixed_buf_list {
-	struct qat_alg_buf_list sgl_hdr;
+	struct qat_alg_buf_list_hdr sgl_hdr;
 	struct qat_alg_buf descriptors[QAT_MAX_BUFF_DESC];
 } __packed __aligned(64);