media: v4l: add missing MODULE_DESCRIPTION() macros

media: v4l: add missing MODULE_DESCRIPTION() macros

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/media/v4l2-core/v4l2-async.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/media/v4l2-core/v4l2-fwnode.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>