Documentation/process: fix a cross reference

The cross-reference for the handbooks section works. However, it is
meant to describe the path inside the Kernel's doc where the section
is, but there's an space instead of a dash, plus it lacks the .rst at
the end, which makes:

	./scripts/documentation-file-ref-check

to complain.

Fixes: 604370e ("Documentation/process: Add maintainer handbooks section")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: mchehab

Documentation/process/submitting-patches.rst

@@ -22,8 +22,8 @@ use it, it will make your life as a kernel developer and in general much
 easier.
 
 Some subsystems and maintainer trees have additional information about
-their workflow and expectations, see :ref:`Documentation/process/maintainer
-handbooks <maintainer_handbooks_main>`.
+their workflow and expectations, see
+:ref:`Documentation/process/maintainer-handbooks.rst <maintainer_handbooks_main>`.
 
 Obtain a current source tree
 ----------------------------