In case of error, the function of_iomap() returns NULL pointer not
ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test..
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>