ASoC: rt1316: Fix return value check in rt1316_sdw_probe()

ASoC: rt1316: Fix return value check in rt1316_sdw_probe()

In case of error, the function devm_regmap_init_sdw() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check should
be replaced with IS_ERR().

Fixes: a262057df513 ("ASoC: rt1316: Add RT1316 SDCA vendor-specific driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210303064041.898281-1-weiyongjun1@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>