Input: Use accessor for MT values

The current MT accessor function does not distinguish between the MT
values and the slot specification event. Add an accessor function for
the values only, and use it where appropriate.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
diff --git a/drivers/input/input.c b/drivers/input/input.c
index 1f78c957..8921c61 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -180,7 +180,7 @@
 		return INPUT_IGNORE_EVENT;
 	}
 
-	is_mt_event = code >= ABS_MT_FIRST && code <= ABS_MT_LAST;
+	is_mt_event = input_is_mt_value(code);
 
 	if (!is_mt_event) {
 		pold = &dev->absinfo[code].value;