selinux: Delete an unnecessary return statement in policydb_destroy()

The script "checkpatch.pl" pointed information out like the following.

WARNING: void function return statements are not generally useful

Thus remove such a statement in the affected function.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/ss/policydb.c

@@ -880,8 +880,6 @@ void policydb_destroy(struct policydb *p)
 	ebitmap_destroy(&p->filename_trans_ttypes);
 	ebitmap_destroy(&p->policycaps);
 	ebitmap_destroy(&p->permissive_map);
-
-	return;
 }
 
 /*