clk: sprd: Switch from of_iomap() to devm_ioremap_resource()

devm_ioremap_resources() automatically requests resources and devm_ wrappers
do better error handling and unmapping of the I/O region when needed,
that would make drivers more clean and simple.

Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
Reviewed-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>