phy: sunplus: Fix an IS_ERR() vs NULL bug in sp_usb_phy_probe

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

Fixes: 99d9ccd9

 ("phy: usb: Add USB2.0 phy driver for Sunplus SP7021")
Signed-off-by: Peng Wu <wupeng58@huawei.com>
Link: https://lore.kernel.org/r/20220911060053.123594-1-wupeng58@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>