docs/devel/kconfig.rst: Fix incorrect markup

docs/devel/kconfig.rst: Fix incorrect markup

In rST markup syntax, the inline markup (*italics*, **bold** and
``monospaced``) must be separated from the surrending text by
non-word characters, otherwise it is not interpreted as markup.
To force interpretation as markup in the middle of a word,
you need to use a backslash-escaped space (which will not
appear as a space in the output).

Fix a missing backslash-space in this file, which meant that the ``
after "select" was output literally and the monospacing was
incorrectly extended all the way to the end of the next monospaced
word.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20230411105424.3994585-1-peter.maydell@linaro.org