input: add valuator_mask_free() to free a valuator mask.

Expecting the caller to free the mask requires us to keep it in a single
memory block (which may be an issue lateron), aside from leaving the API
asymetrical. Provide valuator_mask_free() to free the memory and reset the
mask pointer to NULL.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Fernando Carrijo <fcarrijo@freedesktop.org>
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>

dix/inpututils.c

@@ -433,6 +433,14 @@ valuator_mask_new(int num_valuators)
     return mask;
 }
 
+void
+valuator_mask_free(ValuatorMask **mask)
+{
+    free(*mask);
+    *mask = NULL;
+}
+
+
 /**
  * Sets a range of valuators between first_valuator and num_valuators with
  * the data in the valuators array. All other values are set to 0.