asus-wmi: signedness bug in read_brightness()

"err" needs to be signed for the error handling to work.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
index 5b779a9..a038595 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -946,7 +946,8 @@
 static int read_brightness(struct backlight_device *bd)
 {
 	struct asus_wmi *asus = bl_get_data(bd);
-	u32 retval, err;
+	u32 retval;
+	int err;
 
 	err = asus_wmi_get_devstate(asus, ASUS_WMI_DEVID_BRIGHTNESS, &retval);