clk: qcom: gdsc: add missing error handling

Since commit 7eb231c3 ("PM / Domains: Convert pm_genpd_init() to
return an error code") pm_genpd_init() can return an error which the
caller must handle.

The current error handling was also incomplete as the runtime PM and
regulator use counts were not balanced in all error paths.

Add the missing error handling to the GDSC initialisation to avoid
continuing as if nothing happened on errors.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>