i2c: acpi: 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: KSPP#193
Link: KSPP#218
Link: https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Author: GustavoARSilva

drivers/i2c/i2c-core-acpi.c

@@ -26,7 +26,7 @@ struct gsb_buffer {
 	union {
 		u16	wdata;
 		u8	bdata;
-		u8	data[0];
+		DECLARE_FLEX_ARRAY(u8, data);
 	};
 } __packed;