video: tegra: host: fix integer overflows

job_size() calculates the size of a job structure based on a struct
passed as a ioctl parameter. This calculation was not checked for
overflow.

Bug 1038551

Change-Id: I13d087dbd5aad5fef1c5d13ceb23e50f565acf95
Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Reviewed-on: http://git-master/r/127185
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>