ASoC: rt715-sdca: Fix return value check in rt715_sdca_sdw_probe()

ASoC: rt715-sdca: Fix return value check in rt715_sdca_sdw_probe()

In case of error, the function devm_regmap_init_sdw_mbq() and
devm_regmap_init_sdw() returns ERR_PTR() not NULL. The NULL test
in the return value check should be replaced with IS_ERR().

Fixes: 393c52d2d109 ("ASoC: rt715-sdca: Add RT715 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/20210309131458.1884899-1-weiyongjun1@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>