Newer asics need 64 bit wptrs. If the wptr is now
smaller than the rptr that doesn't indicate a wrap-around
anymore.
v2: integrate Christian's comments.
Signed-off-by: Ken Wang <Qingqing.Wang@amd.com> Reviewed-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>