net: ethernet: adi: adin1110: Check return value of devm_gpiod_get_optional() in...

net: ethernet: adi: adin1110: Check return value of devm_gpiod_get_optional() in adin1110_check_spi()

The devm_gpiod_get_optional() function may return an ERR_PTR in case of
genuine GPIO acquisition errors, not just NULL which indicates the
legitimate absence of an optional GPIO.

Add an IS_ERR() check after the call in adin1110_check_spi(). On error,
return the error code to ensure proper failure handling rather than
proceeding with invalid pointers.

Fixes: 36934cac7aaf ("net: ethernet: adi: adin1110: add reset GPIO")
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20260202040228.4129097-1-nichen@iscas.ac.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>