clk: qcom: gdsc: Capture pm_genpd_add_subdomain result code

clk: qcom: gdsc: Capture pm_genpd_add_subdomain result code

Adding a new clause to this if/else I noticed the existing usage of
pm_genpd_add_subdomain() wasn't capturing and returning the result code.

pm_genpd_add_subdomain() returns an int and can fail. Capture that result
code and throw it up the call stack if something goes wrong.

Fixes: 1b771839de05 ("clk: qcom: gdsc: enable optional power domain support")
Cc: stable@vger.kernel.org
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Link: https://lore.kernel.org/r/20250117-b4-linux-next-24-11-18-clock-multiple-power-domains-v10-2-13f2bb656dad@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>