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: a87a6653 ("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.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/rt1308-sdw.c

@@ -684,8 +684,8 @@ static int rt1308_sdw_probe(struct sdw_slave *slave,
 
 	/* Regmap Initialization */
 	regmap = devm_regmap_init_sdw(slave, &rt1308_sdw_regmap);
-	if (!regmap)
-		return -EINVAL;
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
 
 	rt1308_sdw_init(&slave->dev, regmap, slave);