Delay the registration of VGA switcheroo client to the end of the
probing.  Otherwise a too quick switching may result in Oops during
probing.

Also add the check of the return value from snd_hda_lock_devices().
Reported-and-tested-by: Daniel J Blueman <daniel@quora.org>
Cc: <stable@vger.kernel.org> [v3.5+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>