drm/i915: remove the TODO in pin_and_fence_fb_obj

The copy is async (if there even is one), but when later updating the
GGTT we always sync against the binding, which will in turn sync against
any moves.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Jianshui Yu <jianshui.yu@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221004131916.233474-1-matthew.auld@intel.com