phy: mvebu-cp110-utmi: fix dr_mode property read from dts

The problem with the current implementation is that it does not consider
that the USB controller can have multiple PHY handles with different
arguments count, as for example we have in our cn9131 based platform:
"phys = <&cp0_comphy1 0>, <&cp0_utmi0>;".

In such case calling "of_usb_get_dr_mode_by_phy" with -1 (no phy-cells)
leads to not proper phy detection, taking the "marvell,cp110-utmi-phy"
dts definition we can call the "of_usb_get_dr_mode_by_phy" with 0
(#phy-cells = <0>) and safely look for that phy.

Signed-off-by: Aleksandar Gerasimovski <aleksandar.gerasimovski@belden.com>
Link: https://patch.msgid.link/20260106150643.922110-1-aleksandar.gerasimovski@belden.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>