msm: kgsl: Pass an actual pointer to a snapshot callback

Pass an actual pointer to the snapshot_os callback from
kgsl_device_snapshot in lieu of playing a dangerous dereferencing
trick.

Change-Id: Ic0dedbaddbae90f18953582d113170d316a9b7f4
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>