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

Fixes: c9fe7db6 ("ASoC: amd: Refactoring of DAI from DMA driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20200108035954.51317-1-weiyongjun1@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>