staging: mt7621-pinctrl: init *map to NULL for correct memory assignation

pinctrl_utils_reserve_map() calls krealloc() on *map. Because of this
*map need to be initialized to NULL before calling it.

Fixes: 62b6215c ("staging: mt7621-pinctrl: make use of pinctrl_utils_reserve_map")
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-pinctrl/pinctrl-rt2880.c

@@ -88,6 +88,7 @@ static int rt2880_pinctrl_dt_node_to_map(struct pinctrl_dev *pctrldev,
 	for_each_node_with_property(np_config, "group")
 		ngroups++;
 
+	*map = NULL;
 	ret = pinctrl_utils_reserve_map(pctrldev, map, &reserved_maps,
 					num_maps, ngroups);
 	if (ret) {