ALSA: hda: tas2781-spi: Fix error code in tas2781_read_acpi()

Propagate the error code from devm_gpiod_get_index_optional().  The
current code returns success.

Fixes: bb5f86ea ("ALSA: hda/tas2781: Add tas2781 hda SPI driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/6103e81a-13bf-4eab-89af-f6830c14e14c@stanley.mountain


Signed-off-by: Takashi Iwai <tiwai@suse.de>