selinux: Unify for- and while-loop style

Replace "thing != NULL" comparisons with just "thing" to make
the code look more uniform (mixed styles were used even in the
same source file).

Signed-off-by: Vesa-Matti Kari <vmkari@cc.helsinki.fi>
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/ss/avtab.c

@@ -229,7 +229,7 @@ void avtab_destroy(struct avtab *h)
 
 	for (i = 0; i < h->nslot; i++) {
 		cur = h->htable[i];
-		while (cur != NULL) {
+		while (cur) {
 			temp = cur;
 			cur = cur->next;
 			kmem_cache_free(avtab_node_cachep, temp);