[media] em28xx: Remove redundant dev->ctl_input set

dev->ctl_input() is always set before a call to video_mux(),
but then video_mux() sets it again with the same value.

Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>