soc: qcom: smd-rpm: Replace zero-length array with DECLARE_FLEX_ARRAY() helper

Zero-length arrays are deprecated and we are moving towards adopting
C99 flexible-array members, instead. So, replace zero-length arrays
declarations in anonymous union with the new DECLARE_FLEX_ARRAY()
helper macro.

This helper allows for flexible-array members in unions.

Link: https://github.com/KSPP/linux/issues/193
Link: https://github.com/KSPP/linux/issues/224Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/YzIvNIyPhWaG2DTr@work

drivers/soc/qcom/smd-rpm.c

@@ -75,7 +75,7 @@ struct qcom_rpm_message {
 	__le32 length;
 	union {
 		__le32 msg_id;
-		u8 message[0];
+		DECLARE_FLEX_ARRAY(u8, message);
 	};
 };