[PATCH] UML: fix uptime

The use of signed instead of unsigned here broke the calculations on
negative numbers that are involved in calculating wall_to_monotonic.
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

arch/um/kernel/time_kern.c

@@ -87,7 +87,7 @@ void timer_irq(union uml_pt_regs *regs)
 
 void time_init_kern(void)
 {
-	unsigned long long nsecs;
+	long long nsecs;
 
 	nsecs = os_nsecs();
 	set_normalized_timespec(&wall_to_monotonic, -nsecs / BILLION,