spi: cs42l43: Make handling missing spk-id GPIOs explicit

spi: cs42l43: Make handling missing spk-id GPIOs explicit

gpiod_get_array_optional() for spk-id GPIOs can return NULL, if they are
missing, so do not pass the value to PTR_ERR but instead explicitly
treat NULL as acceptable condition.  The old code was correct, but
misleading because PTR_ERR usually is used on errors.

Reported by Smatch:
  drivers/spi/spi-cs42l43.c:241 cs42l43_get_speaker_id_gpios() warn: passing zero to 'PTR_ERR'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://patch.msgid.link/20250501-n-smatch-fixes-v2-2-d2ad9c1f2e67@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>