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: NJuerg Haefliger <juergh@canonical.com>
Link: https://lore.kernel.org/r/20220517140837.331298-1-juergh@canonical.comSigned-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/Kconfig

 config WARN_MISSING_DOCUMENTS
-
 	bool "Warn if there's a missing documentation file"
 	depends on COMPILE_TEST
 	help
-	   It is not uncommon that a document gets renamed.
-	   This option makes the Kernel to check for missing dependencies,
-	   warning when something is missing. Works only if the Kernel
-	   is built from a git tree.
+	  It is not uncommon that a document gets renamed.
+	  This option makes the Kernel to check for missing dependencies,
+	  warning when something is missing. Works only if the Kernel
+	  is built from a git tree.
 
-	   If unsure, select 'N'.
+	  If unsure, select 'N'.
 
 config WARN_ABI_ERRORS
 	bool "Warn if there are errors at ABI files"
 	depends on COMPILE_TEST
 	help
-	   The files under Documentation/ABI should follow what's
-	   described at Documentation/ABI/README. Yet, as they're manually
-	   written, it would be possible that some of those files would
-	   have errors that would break them for being parsed by
-	   scripts/get_abi.pl. Add a check to verify them.
+	  The files under Documentation/ABI should follow what's
+	  described at Documentation/ABI/README. Yet, as they're manually
+	  written, it would be possible that some of those files would
+	  have errors that would break them for being parsed by
+	  scripts/get_abi.pl. Add a check to verify them.
 
-	   If unsure, select 'N'.
+	  If unsure, select 'N'.