[media] m88ds3103: do not return error from get_frontend() when not ready

Do not return error from get_frontend() when status is queried, but
the frontend didn't lock yet. The proper behavior is to only update the
cache after having a lock.

[mchehab@osg.samsung.com: fix the patch description]
Signed-off-by: Antti Palosaari <crope@iki.fi>

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