media: em28xx: Set GPIOs for non-audio boards when switching input

Fixes changing the Line Out audio source with the video input
on MyGica UTV3 board. Previously, GPIOs were only set in
em28xx_set_audio_source(), which only boards with USB audio
support reach.

Signed-off-by: Nils Rothaug <nils.rothaug@gmx.de>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>