docs: accounting: update delay-accounting.rst reference

docs: accounting: update delay-accounting.rst reference

BugLink: https://bugs.launchpad.net/bugs/1953370
commit 0f60a29c52b515532e6b11dc6b3c9e5b5f7ff2b4 upstream.

The file name: accounting/delay-accounting.rst
should be, instead: Documentation/accounting/delay-accounting.rst.

Also, there's no need to use doc:`foo`, as automarkup.py will
automatically handle plain text mentions to Documentation/
files.

So, update its cross-reference accordingly.

Fixes: fcb501704554 ("delayacct: Document task_delayacct sysctl")
Fixes: c3123552aad3 ("docs: accounting: convert to ReST")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>