Fix the retrn value check which testing the wrong variable
in mmp2_clk_init().

Fixes: 1ec770d9 ("clk: mmp: add mmp2 DT support for clock driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>