media: pixfmt-meta-rkisp1.rst: fix two build warnings

media: pixfmt-meta-rkisp1.rst: fix two build warnings

With Sphinx 2.x: those two warnings are produced:

/devel/v4l/docs/sphinx2/Documentation/output/videodev2.h.rst:6: WARNING: undefined label: v4l2-meta-fmt-rk-isp1-params (if the link has no caption the label must precede a section header)
/devel/v4l/docs/sphinx2/Documentation/output/videodev2.h.rst:6: WARNING: undefined label: v4l2-meta-fmt-rk-isp1-stat-3a (if the link has no caption the label must precede a section header)

The reason is that there's no blank line between the two
identifiers.

Fixes: 3f46cac6787f ("media: admin-guide/pixfmt-meta-rkisp1.rst: pixfmt reference conforming with macro")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>