mfd: max14577: Include missing err.h

Add this header explicitly for IS_ERR and friends.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/max14577.c b/drivers/mfd/max14577.c
index c9859d1..5f13cef 100644
--- a/drivers/mfd/max14577.c
+++ b/drivers/mfd/max14577.c
@@ -18,6 +18,7 @@
  * This driver is based on max8997.c
  */
 
+#include <linux/err.h>
 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/mfd/core.h>