Fix v4l2_fourcc define to use "U" cast to avoid shifting signed 32-bit
value by 31 bits problem. This isn't a problem for kernel builds with
gcc.

This could be problem since this header is part of public API which
could be included for builds using compilers that don't handle this
condition safely resulting in undefined behavior.
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>