ASoC: amd: fix an IS_ERR() vs NULL bug in probe

The devm_ioremap() function returns NULL on error, it doesn't return
error pointers.

Fixes: e550339e ("ASoC: amd: add vangogh i2s controller driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20210727081756.GA19121@kili


Signed-off-by: Mark Brown <broonie@kernel.org>