[media] drxk: change it to use request_firmware_nowait()

The firmware blob may not be available when the driver probes.

Instead of blocking the whole kernel use request_firmware_nowait() and
continue without firmware.

This shouldn't be that bad on drx-k devices, as they all seem to have an
internal firmware. So, only the firmware update will take a little longer
to happen.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>