msm: camera: core: Add flush for offline devices

Add flush for offline devices.

Change-Id: I16cc60cc26cfa225a80aa8627d4148568329d676
Signed-off-by: Junzhe Zou <jnzhezou@codeaurora.org>
Signed-off-by: Suresh Vankadara <svankada@codeaurora.org>
Signed-off-by: Karthik Anantha Ram <kartanan@codeaurora.org>
Signed-off-by: Rajakumar Govindaram <rajakuma@codeaurora.org>