OPP: Fix missing cleanup on error in _opp_attach_genpd()

A recent commit updated the code mistakenly to return directly on
errors, without doing the required cleanups. Fix it.

Fixes: 2a56c462 ("OPP: Fix required_opp_tables for multiple genpds using same table")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202405180016.4fbn86bm-lkp@intel.com/


Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>