scsi: target: tcmu: Replace zero-length array with flexible-array member

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://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arraysSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/target/target_core_user.c

@@ -194,7 +194,7 @@ struct tcmu_tmr {
 
 	uint8_t tmr_type;
 	uint32_t tmr_cmd_cnt;
-	int16_t tmr_cmd_ids[0];
+	int16_t tmr_cmd_ids[];
 };
 
 /*