ASoC: rt1308-sdw: Fix return check for devm_regmap_init_sdw()

ASoC: rt1308-sdw: Fix return check for devm_regmap_init_sdw()

devm_regmap_init_sdw() returns a valid pointer on success or ERR_PTR on
failure which should be checked with IS_ERR. Also use PTR_ERR for
returning error codes.

Reported-by: Takashi Iwai <tiwai@suse.de>
Fixes: a87a6653a28c ("ASoC: rt1308-sdw: add rt1308 SdW amplifier driver")
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200826163340.3249608-3-vkoul@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>