phy: ath79-usb: Fix the main reset name to match the DT binding

I submitted this driver several times before it got accepted. The
first series hasn't been accepted but the DTS binding did made it.
I then made a second series that added generic reset support to the
PHY core, this in turn required a change to the DT binding. This
second series seemed to have been ignored, so I did a third one
without the change to the PHY core and the DT binding update, and this
last attempt finally made it.

But two months later the DT binding update from the second series has
been integrated too. So now the driver doesn't match the binding and
the only DTS using it. This patch fix the driver to match the new
binding.

Signed-off-by: Alban Bedel <albeu@free.fr>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>