docs: dt: fix broken reference to phy-cadence-torrent.yaml

docs: dt: fix broken reference to phy-cadence-torrent.yaml

This file was removed, and another file was added instead of
it, on two separate commits.

Splitting a single logical change (doc conversion) on two
patches is a bad thing, as it makes harder to discover what
crap happened.

Anyway, this patch fixes the broken reference, making it
pointing to the new location of the file.

Fixes: 922003733d42 ("dt-bindings: phy: Remove Cadence MHDP PHY dt binding")
Fixes: c6d8eef38b7f ("dt-bindings: phy: Add Cadence MHDP PHY bindings in YAML format.")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/3f1cf6d74e392f3ee9f894d82cb7ee29d04c1b6d.1586881715.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>