[media] em28xx: check if a device has audio earlier

Better to split chipset detection from the audio setup. So, move the
detection code to em28xx_init_dev().

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

diff --cc drivers/media/usb/em28xx/em28xx-cards.c
Simple merge

diff --cc drivers/media/usb/em28xx/em28xx-core.c
Simple merge