ALSA: fm801: Gracefully handle failure of tuner auto-detect

Commit 96760015


("ALSA: fm801: add error handling if auto-detect fails") seems to
break systems that were previously working without a tuner.

As a bonus, this should fix init and cleanup for the case where the
tuner is explicitly disabled.

Reported-and-tested-by: Hor Jiun Shyong <jiunshyong@gmail.com>
References: http://bugs.debian.org/641946


Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: stable@kernel.org [v3.0+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>