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>

drivers/mfd/sm501.c

@@ -367,7 +367,8 @@ int sm501_unit_power(struct device *dev, unsigned int unit, unsigned int to)
 		break;
 
 	default:
-		return -1;
+		gate = -1;
+		goto already;
 	}
 
 	writel(mode, sm->regs + SM501_POWER_MODE_CONTROL);