ARM: dts: bcm2711-rpi-4-b: Fix usb's unit address

ARM: dts: bcm2711-rpi-4-b: Fix usb's unit address

The unit address is supposed to represent '<device>,<function>'. Which
are both 0 for RPi4b's XHCI controller. On top of that although
OpenFirmware states bus number goes in the high part of the last reg
parameter, FDT doesn't seem to care for it[1], so remove it.

[1] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20210830103909.323356-1-nsaenzju@redhat.com/#24414633
Fixes: 258f92d2f840 ("ARM: dts: bcm2711: Add reset controller to xHCI node")
Suggested-by: Rob Herring <robh@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210831125843.1233488-2-nsaenzju@redhat.com
Signed-off-by: Nicolas Saenz Julienne <nsaenz@kernel.org>