docs: Kconfig: Fix help text indentation

The convention for help text indentation seems to be a single tab followed
by two whitespaces. Do that.

While at it, remove a stray empty line.

Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Link: https://lore.kernel.org/r/20220517140837.331298-1-juergh@canonical.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>