media: allegro-dvt: increase buffer size in msg_type_name()

Fixes this compile error

drivers/media/platform/allegro-dvt/allegro-mail.c: In function 'msg_type_name':
drivers/media/platform/allegro-dvt/allegro-mail.c:37:48: warning: '%04x' directive output may be truncated writing between 4 and 8 bytes into a region of size 6 [-Wformat-truncation=]
   37 |                 snprintf(buf, sizeof(buf), "(0x%04x)", type);
      |                                                ^~~~
drivers/media/platform/allegro-dvt/allegro-mail.c:37:44: note: directive argument in the range [1, 4294967295]
   37 |                 snprintf(buf, sizeof(buf), "(0x%04x)", type);
      |                                            ^~~~~~~~~~
drivers/media/platform/allegro-dvt/allegro-mail.c:37:17: note: 'snprintf' output between 9 and 13 bytes into a destination of size 9
   37 |                 snprintf(buf, sizeof(buf), "(0x%04x)", type);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Michael Tretter <m.tretter@pengutronix.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>