rt2x00: Fix Sparse warning

rt2x00link_reset_qual() is not declared in a header,
and is only internally used within rt2x00link.c.
It should be declared as static.
Signed-off-by: NIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00link.c

@@ -387,7 +387,7 @@ void rt2x00link_reset_tuner(struct rt2x00_dev *rt2x00dev, bool antenna)
 		rt2x00link_antenna_reset(rt2x00dev);
 }
 
-void rt2x00link_reset_qual(struct rt2x00_dev *rt2x00dev)
+static void rt2x00link_reset_qual(struct rt2x00_dev *rt2x00dev)
 {
 	struct link_qual *qual = &rt2x00dev->link.qual;