drm/i915: Increment composite fence seqno

Increment composite fence seqno on each fence creation.

Fixes: 544460c3

 ("drm/i915: Multi-BB execbuf")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211214195913.35735-1-matthew.brost@intel.com