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.
Fixes: a2e230c7b2ea ("clk: Add clock driver for ASPEED BMC SoCs") Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>