doc: timers-howto: fix a typo ("unsgined")

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/timers/timers-howto.txt

@@ -24,7 +24,7 @@ ATOMIC CONTEXT:
 
 	ndelay(unsigned long nsecs)
 	udelay(unsigned long usecs)
-	mdelay(unsgined long msecs)
+	mdelay(unsigned long msecs)
 
 	udelay is the generally preferred API; ndelay-level
 	precision may not actually exist on many non-PC devices.