PM / OPP: Propagate the error returned by _find_opp_table()

Don't send -EINVAL and propagate what's received from _find_opp_table().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>