ima: 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>

security/integrity/ima/ima.h

@@ -101,7 +101,7 @@ struct ima_template_entry {
 	struct tpm_digest *digests;
 	struct ima_template_desc *template_desc; /* template descriptor */
 	u32 template_data_len;
-	struct ima_field_data template_data[0];	/* template related data */
+	struct ima_field_data template_data[];	/* template related data */
 };
 
 struct ima_queue_entry {