media: video: tegra: Update ad5816 focuser driver

media: video: tegra: Update ad5816 focuser driver

Modify code structure and incorporate
few review comments raised in base change
of ad5816 driver implementation.

Bug 947792

Change-Id: I4b9e95669353f6e9bb71f4e172b71b4e31b1f0d7
Signed-off-by: Sudhir Vyas <svyas@nvidia.com>
Reviewed-on: http://git-master/r/105933
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>
Rebase-Id: R4ad0be696ea9f0387c248f54558bfbfb44d88e46