kbuild: correct formatting of header in kbuild module docs

Minor formatting fixup.

Fixes: cd238ef ("docs: kbuild: convert docs to ReST and rename to *.rst")
Signed-off-by: Alex Gaynor <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

Author: alex

Documentation/kbuild/modules.rst

@@ -498,7 +498,8 @@ build.
 	will be written containing all exported symbols that were not
 	defined in the kernel.
 
---- 6.3 Symbols From Another External Module
+6.3 Symbols From Another External Module
+----------------------------------------
 
 	Sometimes, an external module uses exported symbols from
 	another external module. kbuild needs to have full knowledge of