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.