power: pm8921-bms: Cancel/schedule work across suspend/resume

Clean up the work before going into suspend to avoid any
race during resume.

While at it, fix the timing comparison during resume
and use the de-referenced chip pointer.

Change-Id: I9e6dbe49e6ad5ebf1cdf9a3cd0ec7f57aa6495c6
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>