drm/msm/gpu: Don't allow zero fence_id

Elsewhere we treat zero as "no fence" and __msm_gem_submit_destroy()
skips removal from fence_idr.  We could alternately change this to use
negative values for "no fence" but I think it is more clear to not allow
zero as a valid fence_id.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Fixes: a61acbbe ("drm/msm: Track "seqno" fences by idr")
Link: https://lore.kernel.org/r/20211129182344.292609-1-robdclark@gmail.com


Signed-off-by: Rob Clark <robdclark@chromium.org>