pinctrl: devicetree: fix null pointer dereferencing in pinctrl_dt_to_map

In the Linux kernel, the following vulnerability has been resolved:

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.