Don't try to "validate" a non-existing timeval.

settime() with a NULL timeval is silly but legal.

Noticed by Dave Jones <davej@redhat.com>

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/time.c b/kernel/time.c
index 7477b1d..1f23e68 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -155,7 +155,7 @@
 	static int firsttime = 1;
 	int error = 0;
 
-	if (!timespec_valid(tv))
+	if (tv && !timespec_valid(tv))
 		return -EINVAL;
 
 	error = security_settime(tv, tz);