Documentation: maintainer-tip: Rectify link to "Describe your changes" section of submitting-patches.rst

The general changelog rules for the tip tree refers to "Describe your
changes" section of submitting patches guide. However, the internal link
reference targets to non-existent "submittingpatches" label, which
brings reader to the top of the linked doc.

Correct the target. No changes to submitting-patches.rst since the
required label is already there.

Fixes: 31c9d7c8 ("Documentation/process: Add tip tree handbook")
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230320124327.174881-1-bagasdotme@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>