FROMLIST: thermal: Fix NULL pointer dereference issue

Cooling stats variable inside thermal_cooling_device_stats_update()
can get NULL. We should add a valid check on stat before using it.

Bug: 173355233
Link: https://lore.kernel.org/lkml/1605544181-5348-1-git-send-email-mojha@codeaurora.org/


Change-Id: I48105dcf8ff81d272534c59b7120a6d9fc831d04
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>