media: dvb-usb: add missing MODULE_DESCRIPTION() macros

With ARCH=x86, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/media/usb/dvb-usb/dvb-usb-dibusb-common.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/media/usb/dvb-usb/dvb-usb-dibusb-mc-common.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>