docs: process: fix a typoed cross-reference

Commit 329ac9af added a cross-reference missing a hyphen; add one from
my emergency hyphen stash.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 329ac9af ("docs: submitting-patches: Discuss interleaved replies")
Closes: https://lore.kernel.org/oe-kbuild-all/202305201652.POM84URe-lkp@intel.com/


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