USB: gadget: udc: s3c2410_udc: fix return value check in s3c2410_udc_probe()

USB: gadget: udc: s3c2410_udc: fix return value check in s3c2410_udc_probe()

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

Fixes: 5bc394c227de ("usb: gadget: s3c: use platform resources")
Cc: stable <stable@vger.kernel.org>
Reported-by: Hulk Robot <hulkci@huawei.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210305034927.3232386-1-weiyongjun1@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>