bearch: Remove unnecessary test in arch_perform_memory_operand().

When arch_perform_memory_operand() returned a positive result before, there really should be a callback to actually perform the action.

ir/be/bearch.c

@@ -84,12 +84,7 @@ int arch_possible_memory_operand(const ir_node *irn, unsigned int i)
 void arch_perform_memory_operand(ir_node *irn, ir_node *spill, unsigned int i)
 {
 	const arch_irn_ops_t *ops = get_irn_ops(irn);
-
-	if (ops->perform_memory_operand) {
-		ops->perform_memory_operand(irn, spill, i);
-	} else {
-		return;
-	}
+	ops->perform_memory_operand(irn, spill, i);
 }
 
 int arch_get_op_estimated_cost(const ir_node *irn)