drm/xe: Use a small negative initial seqno

Causes an early 32-bit wrap and may thus help CI catch wrapping errors
that may otherwise not show early enough.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>