media: imx7.rst: Fix ReST syntax

Sphinx didn't like the code-blocks on this file:

	Documentation/media/v4l-drivers/imx7.rst:19: WARNING: Inline substitution_reference start-string without end-string.
	Documentation/media/v4l-drivers/imx7.rst:20: WARNING: Block quote ends without a blank line; unexpected unindent.
	Documentation/media/v4l-drivers/imx7.rst:27: WARNING: Inline substitution_reference start-string without end-string.
	Documentation/media/v4l-drivers/imx7.rst:79: WARNING: Error in "code-block" directive:
	maximum 1 argument(s) allowed, 26 supplied.

	.. code-block:: none
	   # Setup links
	<snip/>
	   media-ctl -V "'csi':0 [fmt:SBGGR10_1X10/800x600 field:none]"
	Documentation/media/v4l-drivers/imx7.rst:96: WARNING: Error in "code-block" directive:
	maximum 1 argument(s) allowed, 9 supplied.

	.. code-block:: none
	<snip/>.
	                    -> "imx7-mipi-csis.0":0 [ENABLED]

Fix them, in order to match the expected syntax for code blocks.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>