OPP: Don't drop opp_table->np reference while it is still in use

OPP: Don't drop opp_table->np reference while it is still in use

The OPP table contains a reference of the DT node, opp_table->np,
throughout its lifetime. We shouldn't drop the refcount for the same
from _of_init_opp_table(), but do that while removing the OPP table
finally.

Signed-off-by: Liang He <windhl@126.com>
[ Viresh: Updated subject / commit log and drop reference from
	  _of_clear_opp_table() ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>