media: venus: hfi_msgs.h: 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
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

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 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/platform/qcom/venus/hfi_msgs.h

@@ -155,7 +155,7 @@ struct hfi_msg_session_empty_buffer_done_pkt {
 	u32 input_tag;
 	u32 packet_buffer;
 	u32 extradata_buffer;
-	u32 data[0];
+	u32 data[];
 };
 
 struct hfi_msg_session_fbd_compressed_pkt {
@@ -175,7 +175,7 @@ struct hfi_msg_session_fbd_compressed_pkt {
 	u32 picture_type;
 	u32 packet_buffer;
 	u32 extradata_buffer;
-	u32 data[0];
+	u32 data[];
 };
 
 struct hfi_msg_session_fbd_uncompressed_plane0_pkt {
@@ -202,7 +202,7 @@ struct hfi_msg_session_fbd_uncompressed_plane0_pkt {
 	u32 picture_type;
 	u32 packet_buffer;
 	u32 extradata_buffer;
-	u32 data[0];
+	u32 data[];
 };
 
 struct hfi_msg_session_fbd_uncompressed_plane1_pkt {
@@ -211,7 +211,7 @@ struct hfi_msg_session_fbd_uncompressed_plane1_pkt {
 	u32 filled_len;
 	u32 offset;
 	u32 packet_buffer2;
-	u32 data[0];
+	u32 data[];
 };
 
 struct hfi_msg_session_fbd_uncompressed_plane2_pkt {
@@ -220,7 +220,7 @@ struct hfi_msg_session_fbd_uncompressed_plane2_pkt {
 	u32 filled_len;
 	u32 offset;
 	u32 packet_buffer3;
-	u32 data[0];
+	u32 data[];
 };
 
 struct hfi_msg_session_parse_sequence_header_done_pkt {