msm: vidc: make venus_hfi_device as a static variable

1. Mostly venus_hfi_device ptr is derived from hal_session
   (session->device). During session close hal_session is
   freed in forward path and at the same time RBR arrives
   at feed_back path leads to race condition.
2. If forward threads acquires device->lock first then
   reverse thread may have stale device ptr(which is already
   freed), accessing that ptr leads to device crash
3. To avoid refrencing device from hal_session, made
   venus_hfi_device as a static variable within hfi_common

Change-Id: Ic5db6d4f6da6da08e16f4f00a06a3c4fec4f9c6e
Signed-off-by: Govindaraj Rajagopal <grajagop@codeaurora.org>