drm/v3d: Drop reservation of a shared slot in the dma-buf reservations.

We only set the excl (possible-writing) fence pointer and never add a
shared (read-only) fence.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190416225856.20264-5-eric@anholt.net


Acked-by: Rob Clark <robdclark@gmail.com>