Since the commit c647f806 ("ALSA: hda - Allow multiple ADCs for
mic mute LED controls") we allow enabling the mic mute LED with
multiple ADCs.  The commit changed the function return value to be
zero or a negative error, while this change was overlooked in the
thinkpad_acpi helper code where it still expects a positive return
value for success.  This eventually leads to a NULL dereference on a
system that has only a mic mute LED.

This patch corrects the return value check in the corresponding code
as well.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201621
Fixes: c647f806 ("ALSA: hda - Allow multiple ADCs for mic mute LED controls")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>