smf: fix null-check in get_child_of()

Co-authored-by: Keith Short <[email protected]>

Author: vlad-kulikov

lib/smf/smf.c

@@ -38,7 +38,7 @@ static const struct smf_state *get_child_of(const struct smf_state *states,
 {
 	const struct smf_state *state = states;
 
-	while (state) {
+	while (state != NULL) {
 		if (state->parent == parent) {
 			return state;
 		}