spi: aspeed: Fix an IS_ERR() vs NULL bug in probe()

The platform_get_resource() function doesn't return error pointers, it
returns NULL on error.  Update the error checking to match.

Fixes: 64d87ccfae33 ("spi: aspeed: Only map necessary address window region")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/aPJpEnfK31pHz8_w@stanley.mountain
Signed-off-by: Mark Brown <broonie@kernel.org>
1 file changed