spelling fixes: arch/um/

Spelling fixes in arch/um/.

Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
Acked-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
index 277fce1..70c2d62 100644
--- a/arch/um/kernel/irq.c
+++ b/arch/um/kernel/irq.c
@@ -326,7 +326,7 @@
 }
 
 /*
- * do_IRQ handles all normal device IRQ's (the special
+ * do_IRQ handles all normal device IRQs (the special
  * SMP cross-CPU interrupts have their own specific
  * handlers).
  */