irgmod: Correct typo in comment.

ir/ir/irgmod.c

@@ -35,7 +35,7 @@ void exchange(ir_node *old, ir_node *nw)
 	ir_graph *irg = get_irn_irg(old);
 	assert(irg == get_irn_irg(nw));
 #ifndef NDEBUG
-	/* When replacing a PhiM node, it must not be hold by a keep-alive edge.
+	/* When replacing a PhiM node, it must not be held by a keep-alive edge.
 	 * => Keep-alive edges are not normal users and should not move along when
 	 * exchanging. */
 	if (is_Phi(old) && get_Phi_loop(old) && !(is_Phi(nw) && get_Phi_loop(nw))