msm: vidc: Add same fd ref only for static buffer mode

Add same fd ref only for static buffer mode.
Driver is configured for dynamic buffer mode by
default on Venus 3xx targets. If client uses the
same fd for all output buffers, then the first
buffer can remain mapped without reference, which
is incompatible with the curently logic which
assumes buffers to have a reference if they are
already mapped

CRs-Fixed: 773605
Change-Id: I025fe373532e185660d43bae28457cbf06f20e7a
Signed-off-by: Surajit Podder <spodder@codeaurora.org>