msm: ispif: Assign file ops table and remove redundant pointer conversion

Fix the following two issues:

1. Remove the redundant pointer conversion from 32bit space to 64bit
space.

2. Assign the file operations table pointer to the subdevice file
operations.

Change-Id: I12e5ee43464b7780f2e929347f491c19961f72ba
Signed-off-by: Seemanta Dutta <seemanta@codeaurora.org>