oprofile: 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] KSPP/linux#21

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/oprofile/cpu_buffer.h

@@ -33,7 +33,7 @@ void flush_cpu_work(void);
 struct op_sample {
 	unsigned long eip;
 	unsigned long event;
-	unsigned long data[0];
+	unsigned long data[];
 };
 
 struct op_entry;