drm/bridge/mhl.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: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200305110011.GA21056@embeddedor

include/drm/bridge/mhl.h

@@ -327,13 +327,13 @@ struct mhl_burst_bits_per_pixel_fmt {
 	struct {
 		u8 stream_id;
 		u8 pixel_format;
-	} __packed desc[0];
+	} __packed desc[];
 } __packed;
 
 struct mhl_burst_emsc_support {
 	struct mhl3_burst_header hdr;
 	u8 num_entries;
-	__be16 burst_id[0];
+	__be16 burst_id[];
 } __packed;
 
 struct mhl_burst_audio_descr {