clk: qcom: Fix return value check in apss_ipq6018_probe()

clk: qcom: Fix return value check in apss_ipq6018_probe()

In case of error, the function dev_get_regmap() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check should be
replaced with NULL test.

Fixes: 5e77b4ef1b19 ("clk: qcom: Add ipq6018 apss clock controller")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20200628023055.50608-1-weiyongjun1@huawei.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>