OPP: Fix support for required OPPs for multiple PM domains

It has turned out that having _set_required_opps() to recursively call
dev_pm_opp_set_opp() to set the required OPPs, doesn't really work as well
as we expected.

More precisely, at each recursive call to dev_pm_opp_set_opp() we are
changing an OPP for a required_dev that belongs to a required-OPP table.
The problem with this, is that we may have several devices sharing the same
required-OPP table, which leads to an incorrect behaviour in regards to
aggregating the per device votes.

To fix the problem for a required-OPP table belonging to a PM domain, which
is the only existing usecase for now, let's simply replace the call to
dev_pm_opp_set_opp() in _set_required_opps() by a call to _set_opp_level().

Moving forward we may potentially need to add support for other types of
required-OPP tables. In this case, the aggregation needs to be thought of.

Fixes: e37440e7 ("OPP: Call dev_pm_opp_set_opp() for required OPPs")
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/20240822224547.385095-2-ulf.hansson@linaro.org