drbd: Replace zero-length array with flexible-array

There is a regular need in the kernel to provide a way to declare having a
dynamically sized set of trailing elements in a structure. Kernel code should
always use “flexible array members”[1] for these cases. The older style of
one-element or zero-length arrays should no longer be used[2].

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://github.com/KSPP/linux/issues/21

Signed-off-by: Gustavo A. R. Silva <[e-mail]>

drivers/block/drbd/drbd_int.h

···
 	unsigned int head_index;
 	unsigned int size;
 	int total; /* sum of all values */
-	int values[0];
+	int values[];
 };
 extern struct fifo_buffer *fifo_alloc(unsigned int fifo_size);
 

drivers/block/drbd/drbd_protocol.h

···
 	u32 resync_rate;
 
 	      /* Since protocol version 88 and higher. */
-	char verify_alg[0];
+	char verify_alg[];
 } __packed;
 
 struct p_rs_param_89 {
···
 	u32 two_primaries;
 
 	/* Since protocol version 87 and higher. */
-	char integrity_alg[0];
+	char integrity_alg[];
 
 } __packed;
 
···
 	u16	    dds_flags; /* use enum dds_flags here. */
 
 	/* optional queue_limits if (agreed_features & DRBD_FF_WSAME) */
-	struct o_qlim qlim[0];
+	struct o_qlim qlim[];
 } __packed;
 
 struct p_state {
···
 	 */
 	u8 encoding;
 
-	u8 code[0];
+	u8 code[];
 } __packed;
 
 struct p_delay_probe93 {