power: qpnp-qg: Fix the possible deadlock during suspend

There is a possible deadlock with two-threads (suspend callback
and sleep_work) are holding/waiting on the same mutex.

Fix this by cancelling the work before the mutex is held by
the suspend callback.

Change-Id: I65882067783100e7b9ecdc1e697b93948945b41b
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>