PM / OPP: Free resources and properly return error on failure

_of_init_opp_table_v2() isn't freeing up resources on some errors and
the error values returned are also not correct always.

This fixes following problems:
- Return -ENOENT, if no entries are found in the table.
- Use IS_ERR() to properly check return value of _find_device_opp().
- Return error value with PTR_ERR() in above case.
- Free table if _find_device_opp() fails.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>