ARM: mvebu: fix usb@ unit address on Armada 38x to match register address

On Marvell Armada 38x, the USB2 controller registers are at 0x58000,
so the corresponding Device Tree node should have a unit address of
58000, and not 50000. We were using 50000 due to an incorrect
copy/pastebin of Armada 370/XP code.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>