mfd: sm501, fix lock imbalance

Add omitted unlock in sm501_unit_power.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/sm501.c b/drivers/mfd/sm501.c
index 4c7b796..0cc5eef 100644
--- a/drivers/mfd/sm501.c
+++ b/drivers/mfd/sm501.c
@@ -367,7 +367,8 @@
 		break;
 
 	default:
-		return -1;
+		gate = -1;
+		goto already;
 	}
 
 	writel(mode, sm->regs + SM501_POWER_MODE_CONTROL);