media: hantro: h264: Fix a comment in b1_ref_list_cmp()

So it matches the code and the spec.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Francois Buergisser <fbuergisser@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>