firmware: arm_scmi: 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/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://lore.kernel.org/r/20220401075537.2407376-1-lv.ruyi@zte.com.cnReported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/clock.c

@@ -49,7 +49,7 @@ struct scmi_msg_resp_clock_describe_rates {
 	struct {
 		__le32 value_low;
 		__le32 value_high;
-	} rate[0];
+	} rate[];
 #define RATE_TO_U64(X)		\
 ({				\
 	typeof(X) x = (X);	\