raid6: riscv: Prevent compiler from breaking inline vector assembly code

To prevent the compiler from breaking the inline vector assembly code,
this code must be built without compiler support for vector.

Signed-off-by: Chunyan Zhang <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
[[e-mail]: cleaned up commit message]
Signed-off-by: Paul Walmsley <[e-mail]>

lib/raid6/rvv.c

···
 	return has_vector();
 }
 
+#ifdef __riscv_vector
+#error "This code must be built without compiler support for vector"
+#endif
+
 static void raid6_rvv1_gen_syndrome_real(int disks, unsigned long bytes, void **ptrs)
 {
 	u8 **dptr = (u8 **)ptrs;