pm: fix try_to_freeze_tasks()'s use of do_div()

Fix try_to_freeze_tasks()'s use of do_div() on an s64 by making
elapsed_csecs64 a u64 instead and dividing that.

Possibly this should be guarded lest the interval calculation turn up
negative, but the possible negativity of the result of the division is
cast away anyway.

This was introduced by patch 438e2ce68d.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/power/process.c

@@ -149,7 +149,7 @@ static int try_to_freeze_tasks(bool sig_only)
 	unsigned long end_time;
 	unsigned int todo;
 	struct timeval start, end;
-	s64 elapsed_csecs64;
+	u64 elapsed_csecs64;
 	unsigned int elapsed_csecs;
 
 	do_gettimeofday(&start);