drm/xe/ufence: Wake up waiters after setting ufence->signalled

drm/xe/ufence: Wake up waiters after setting ufence->signalled

If a previous ufence is not signalled, vm_bind will return -EBUSY.
Delaying the modification of ufence->signalled can cause issues if the
UMD reuses the same ufence so update ufence->signalled before waking up
waiters.

Cc: Matthew Brost <matthew.brost@intel.com>
Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3233
Fixes: 977e5b82e090 ("drm/xe: Expose user fence from xe_sync_entry")
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241114150537.4161573-1-nirmoy.das@intel.com
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>