mfd: AB3100 propagate error

This makes ab3100_set_register_interruptible() propagate the error
code from suboperations properly so it can be handles properly.
(A special case comes from signal interruption.)

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/ab3100-core.c b/drivers/mfd/ab3100-core.c
index ffe4b64..377ec2b 100644
--- a/drivers/mfd/ab3100-core.c
+++ b/drivers/mfd/ab3100-core.c
@@ -107,7 +107,7 @@
 		err = 0;
 	}
 	mutex_unlock(&ab3100->access_mutex);
-	return 0;
+	return err;
 }
 EXPORT_SYMBOL(ab3100_set_register_interruptible);