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>
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
index 71b8c94..47a09ee 100644
--- a/arch/um/kernel/irq.c
+++ b/arch/um/kernel/irq.c
@@ -297,6 +297,13 @@
 	return 1;
 }
 
+void um_free_irq(unsigned int irq, void *dev)
+{
+	free_irq_by_irq_and_dev(irq, dev);
+	free_irq(irq, dev);
+}
+EXPORT_SYMBOL(um_free_irq);
+
 int um_request_irq(unsigned int irq, int fd, int type,
 		   irq_handler_t handler,
 		   unsigned long irqflags, const char * devname,