firmware: arm_scmi: driver: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertenly introduced[3] to the codebase from now on.

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

---
 drivers/firmware/arm_scmi/driver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 8f952f2f1a29..b40f71edc92d 100644
@@ -148,7 +148,7 @@ struct scmi_shared_mem {
 #define SCMI_SHMEM_FLAG_INTR_ENABLED	BIT(0)
 	__le32 length;
 	__le32 msg_header;
-	u8 msg_payload[0];
+	u8 msg_payload[];
 };
 
 static const int scmi_linux_errmap[] = {

2.25.0

Applied these 3 patches [0][1][2] for v5.7

--
Regards,
Sudeep

[0]: https://lore.kernel.org/r/20200211231604.GA17274@embeddedor
[1]: https://lore.kernel.org/r/20200211231252.GA14830@embeddedor
[2]: https://lore.kernel.org/r/20200211231045.GA13956@embeddedor

Thanks, Sudeep.
--
Gustavo