power: smb1390: Add snapshot of driver

Add snapshot of the SMB1390 driver as of msm-4.14
'commit 2af01acb8e045 ("clk: qcom: gdsc: Remove global mutex lock in
enable/disable callbacks")'.

Changed use of cancel_work() to cancel_work_sync() as the former has
been made obsolete.

Change-Id: I94b8075ad940023e3f67169b1fba0142ca028569
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>