9p: Fix Kconfig indentation

Adjust indentation from spaces to tab (+optional two spaces) as in
coding style with command like:
	$ sed -e 's/^        /\t/' -i */Kconfig

Link: http://lkml.kernel.org/r/20191120134340.16770-1-krzk@kernel.orgSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>