firmware: qcom: scm: Return PTR_ERR when devm_clk_get fails

When devm_clk_get fails for core clock, the failure was ignored
and the core_clk was explicitly set to NULL so that other
remaining clocks can be queried. However, now that we have a
cleaner way of expressing the clock dependency, return failure
when devm_clk_get fails for core clock.

Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>