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: 2a56c46 ("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>

Author: vireshk

drivers/opp/core.c

@@ -2443,8 +2443,10 @@ static int _opp_attach_genpd(struct opp_table *opp_table, struct device *dev,
 		 * Cross check it again and fix if required.
 		 */
 		gdev = dev_to_genpd_dev(virt_dev);
-		if (IS_ERR(gdev))
-			return PTR_ERR(gdev);
+		if (IS_ERR(gdev)) {
+			ret = PTR_ERR(gdev);
+			goto err;
+		}
 
 		genpd_table = _find_opp_table(gdev);
 		if (!IS_ERR(genpd_table)) {