V4L/DVB (10659): em28xx: register device to soundcard for sysfs

As explained in "Writing an ALSA driver" (T. Iwai), audio drivers should
set the struct device for the card before registering the card instance.
This will add the correct /sys/class/sound/cardN/device symlink, so HAL
can see the device and ConsoleKit sets its ACL permissions for the
logged-in user.

For em28xx audio capture cards found e.g. in Hauppauge WinTV-HVR-900 (R2),
this patch fixes errors like:

ALSA lib pcm_hw.c:1429:(_snd_pcm_hw_open) Invalid value for card
Error opening audio: Permission denied

when running mplayer as a normal user.

Signed-off-by: Nicola Soranzo <nsoranzo@tiscali.it>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>