um: Implement um_free_irq()

Instead of using chip->release() we can achieve the same
using a simple wrapper for free_irq().
We have already um_request_irq(), so um_free_irq() is the perfect
counterpart.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

arch/um/drivers/line.c

@@ -699,7 +699,7 @@ struct winch {
 static void __free_winch(struct work_struct *work)
 {
 	struct winch *winch = container_of(work, struct winch, work);
-	free_irq(WINCH_IRQ, winch);
+	um_free_irq(WINCH_IRQ, winch);
 
 	if (winch->pid != -1)
 		os_kill_process(winch->pid, 1);