[PATCH] uml: fix warning for unused var

That var is used only when CONFIG_UML_REAL_TIME_CLOCK is on, so #ifdef its
definition.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/kernel/time_kern.c

@@ -44,7 +44,9 @@ int timer_irq_inited = 0;
 
 static int first_tick;
 static unsigned long long prev_usecs;
+#ifdef CONFIG_UML_REAL_TIME_CLOCK
 static long long delta;   		/* Deviation per interval */
+#endif
 
 #define MILLION 1000000
 
@@ -60,7 +62,7 @@ void timer_irq(union uml_pt_regs *regs)
 	}
 
 	if(first_tick){
-#if defined(CONFIG_UML_REAL_TIME_CLOCK)
+#ifdef CONFIG_UML_REAL_TIME_CLOCK
 		/* We've had 1 tick */
 		unsigned long long usecs = os_usecs();