docs: submitting-patches: Fix crossref to 'The canonical patch format'

The reference to `explicit_in_reply_to` is pointless as when the
reference was added in the form of "#15" [1], Section 15) was "The
canonical patch format".
The reference of "#15" had not been properly updated in a couple of
reorganizations during the plain-text SubmittingPatches era.

Fix it by using `the_canonical_patch_format`.

[1]: 2ae19acaa50a ("Documentation: Add "how to write a good patch summary" to SubmittingPatches")

Signed-off-by: Akira Yokosawa <[email protected]>
Fixes: 5903019b2a5e ("Documentation/SubmittingPatches: convert it to ReST markup")
Fixes: 9b2c76777acc ("Documentation/SubmittingPatches: enrich the Sphinx output")
Cc: Jonathan Corbet <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Cc: [email protected] # v4.9+
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>

0 files changed, 0 insertions, 0 deletions