msm: camera: crm: Fix cache operation failure

In case of zero device count in camera memory map function
length field is not updated and it leads to no cache operations
are performed and leads to corrupted frame.

Get length based on ion fd and use this field in cache operation
to fix the issue.

Change-Id: Ifecc50b79f59068c463decf29179ef24b618fee4
Signed-off-by: Suresh Vankadara <svankada@codeaurora.org>