Input: mt: add input_mt_is_used

This patch extracts the test (slot->frame == mt->frame) so that it can
be used in third party drivers.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/include/linux/input/mt.h b/include/linux/input/mt.h
index cc5cca7..2e86bd0 100644
--- a/include/linux/input/mt.h
+++ b/include/linux/input/mt.h
@@ -69,6 +69,12 @@
 	return input_mt_get_value(slot, ABS_MT_TRACKING_ID) >= 0;
 }
 
+static inline bool input_mt_is_used(const struct input_mt *mt,
+				    const struct input_mt_slot *slot)
+{
+	return slot->frame == mt->frame;
+}
+
 int input_mt_init_slots(struct input_dev *dev, unsigned int num_slots,
 			unsigned int flags);
 void input_mt_destroy_slots(struct input_dev *dev);