video: fix Coverity missing break issue

Fix:
>>>  CID 280902:  Control flow issues  (MISSING_BREAK)
>>>  The case for value "VIDEO_BPP32" is not terminated
>>>  by a 'break' statement.

Also fix
error: control reaches end of non-void function [-Werror=return-type]

Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>