PM / OPP: Make _find_opp_table_unlocked() static

Fixes the following sparse warning:

drivers/base/power/opp/core.c:49:18: warning:
symbol '_find_opp_table_unlocked' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <[e-mail]>
Reviewed-by: Stephen Boyd <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/base/power/opp/core.c

···
 	return NULL;
 }
 
-struct opp_table *_find_opp_table_unlocked(struct device *dev)
+static struct opp_table *_find_opp_table_unlocked(struct device *dev)
 {
 	struct opp_table *opp_table;