pinctrl: devicetree: don't free uninitialized dev_name on error path

dt_remember_or_free_map() duplicates dev_name for each map entry. If
kstrdup_const() fails, dt_free_map() frees dev_name in all num_maps
entries, including entries that have not been initialized.

Some pinctrl drivers, including pinctrl-imx, allocate the map with
kmalloc() and leave dev_name for the core to initialize. The untouched
entries therefore contain uninitialized data which is passed to
kfree_const().

Reproduced on qemu's mcimx6ul-evk (pinctrl-imx) with failslab injection
while binding the pinctrl-consuming device, under KASAN:

  BUG: KASAN: double-free in dt_free_map+0x34/0xa4
  Free of addr c425a900 by task init/1
   kfree from dt_free_map+0x34/0xa4
   dt_free_map from dt_remember_or_free_map+0x184/0x198
   dt_remember_or_free_map from pinctrl_dt_to_map+0x33c/0x4c8
   pinctrl_dt_to_map from create_pinctrl+0x9c/0x5c0

Initialize all dev_name fields to NULL before duplicating the device
name, making the full-map cleanup safe after a partial failure.

Fixes: be4c60b563 ("pinctrl: devicetree: Avoid taking direct reference to device name string")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>

drivers/pinctrl/devicetree.c

@@ -69,6 +69,10 @@ static int dt_remember_or_free_map(struct pinctrl *p, const char *statename,
 	int i;
 	struct pinctrl_dt_map *dt_map;
 
+	/* Initialize dev_name before any allocation can fail */
+	for (i = 0; i < num_maps; i++)
+		map[i].dev_name = NULL;
+
 	/* Initialize common mapping table entry fields */
 	for (i = 0; i < num_maps; i++) {
 		const char *devname;