clk: sprd: Add check for return value of sprd_clk_regmap_init()

sprd_clk_regmap_init() doesn't always return success, adding check
for its return value should make the code more strong.

Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
Reviewed-by: Baolin Wang <baolin.wang@linaro.org>
[sboyd@kernel.org: Add a missing int ret]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>