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

Fixes: bbb336f3 ("spi: spi-amd: Add AMD SPI controller driver support")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20200429025426.167664-1-weiyongjun1@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>