pinctrl: devicetree: fix null pointer dereferencing in pinctrl_dt_to_map

[ Upstream commit 91d5c506 ]

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.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>