ALSA: hda: uninitialized variable fix

Commit eaa9b3a7 introduced the following
uninitialized warning:

	sound/pci/hda/patch_realtek.c: In function 'set_capture_mixer':
	sound/pci/hda/patch_realtek.c:4928: warning: 'pin' is used uninitialized in this function
	sound/pci/hda/patch_realtek.c:4918: note: 'pin' was declared here

It appears indeed that 'pin' needs to be initialized to 0.

Signed-off-by: Frederik Deweerdt <frederik.deweerdt@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>