docs: fix process/submit-checklist.rst Sphinx warning

add missing indent whitespace to list item, fixes the warning:

- process/submit-checklist.rst:41: WARNING: Enumerated list ends without a blank
  line; unexpected unindent.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
Reviewed-by: Darren Hart (VMware) <dvhart@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/process/submit-checklist.rst

@@ -38,8 +38,8 @@ and elsewhere regarding submitting Linux kernel patches.
    your patch.
 
 6) Any new or modified ``CONFIG`` options do not muck up the config menu and
-  default to off unless they meet the exception criteria documented in
+   default to off unless they meet the exception criteria documented in
-  ``Documentation/kbuild/kconfig-language.txt`` Menu attributes: default value.
+   ``Documentation/kbuild/kconfig-language.txt`` Menu attributes: default value.
 
 7) All new ``Kconfig`` options have help text.