Documentation: process: Correct numbering

Renumber the steps in submit-checklist.rst as some numbers were skipped.

Signed-off-by: Milan Lakhani <milan.lakhani@codethink.co.uk>
Link: https://lore.kernel.org/r/1608064956-5512-1-git-send-email-milan.lakhani@codethink.co.uk


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