mtd: sst25l, fix lock imbalance

Add an omitted unlock to one sst25l_erase fail path.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/devices/sst25l.c

@@ -180,8 +180,10 @@ static int sst25l_erase(struct mtd_info *mtd, struct erase_info *instr)
 	mutex_lock(&flash->lock);
 
 	err = sst25l_wait_till_ready(flash);
-	if (err)
+	if (err) {
+		mutex_unlock(&flash->lock);
 		return err;
+	}
 
 	while (addr < end) {
 		err = sst25l_erase_sector(flash, addr);