power: qpnp-fg: Use cancel_delayed_work_sync for suspend work

This follows the original status before the wakeup sources
are added. In previous cleanups, I did not revert this.

This will help avoid some corner cases that cause instability.

Signed-off-by: Wang Han <416810799@qq.com>
(cherry picked from commit 3465c071edd3ed3ccbb0fdfdc1c2f5c6dfeff0ec)