V4L/DVB (13321): radio-gemtek-pci: fix double mutex_lock

Double mutexlock found by the Linux Driver Verification project and
reported by Alexander Strakh.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
CC: stable@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/radio/radio-gemtek-pci.c

@@ -181,12 +181,10 @@ static void gemtek_pci_mute(struct gemtek_pci *card)
 
 static void gemtek_pci_unmute(struct gemtek_pci *card)
 {
-	mutex_lock(&card->lock);
 	if (card->mute) {
 		gemtek_pci_setfrequency(card, card->current_frequency);
 		card->mute = false;
 	}
-	mutex_unlock(&card->lock);
 }
 
 static int gemtek_pci_getsignal(struct gemtek_pci *card)