PM: Fix signed/unsigned warning in dpm_show_time()

Seen on MIPS32, gcc 4.4.3, 2.6.36-rc4:

drivers/base/power/main.c: In function 'dpm_show_time':
drivers/base/power/main.c:415: warning: comparison of distinct pointer types lacks a cast

do_div() takes unsigned parameters:

uint32_t do_div(uint64_t *n, uint32_t base);

Using an unsigned variable for usecs64 should not cause any problems,
because calltime >= starttime .
Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

drivers/base/power/main.c

@@ -407,7 +407,7 @@ static void pm_dev_err(struct device *dev, pm_message_t state, char *info,
 static void dpm_show_time(ktime_t starttime, pm_message_t state, char *info)
 {
 	ktime_t calltime;
-	s64 usecs64;
+	u64 usecs64;
 	int usecs;
 
 	calltime = ktime_get();