pinctrl: devicetree: fix null pointer dereferencing in pinctrl_dt_to_map

Here is the BUG report by KASAN about null pointer dereference:

BUG: KASAN: null-ptr-deref in strcmp+0x2e/0x50
Read of size 1 at addr 0000000000000000 by task python3/2640
Call Trace:
 strcmp
 __of_find_property
 of_find_property
 pinctrl_dt_to_map

kasprintf() would return NULL pointer when kmalloc() fail to allocate.
So directly return ENOMEM, if kasprintf() return NULL pointer.

Fixes: 57291ce2 ("pinctrl: core device tree mapping table parsing support")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Link: https://lore.kernel.org/r/20221110082056.2014898-1-zengheng4@huawei.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/devicetree.c

@@ -220,6 +220,8 @@ int pinctrl_dt_to_map(struct pinctrl *p, struct pinctrl_dev *pctldev)
 	for (state = 0; ; state++) {
 		/* Retrieve the pinctrl-* property */
 		propname = kasprintf(GFP_KERNEL, "pinctrl-%d", state);
+		if (!propname)
+			return -ENOMEM;
 		prop = of_find_property(np, propname, &size);
 		kfree(propname);
 		if (!prop) {