soc: qcom: Fix a IS_ERR() vs NULL bug in probe

The devm_ioremap() function returns NULL on error, it never returns
error pointers.

Fixes: a77b2a0b ("soc: qcom: Introduce RPM master stats driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/ZH7sgpLAN23bCz9v@moroto