powerpc/83xx: Remove second USB node from SBC834x DTS

Since only one of the SoC USB devices is brought out to a physical
connector on the board, remove the 2nd (USB-DR) node from the DTS.
Having it present and USB enabled will cause a hang at boot.

Signed-off-by: Liang Li <liang.li@windriver.com>
Signed-off-by: Yang Shi <yang.shi@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>