[POWERPC] 83xx: Fix wrong USB phy type in mpc837xrdb dts

Due to chip constraint MPC837x USB DR module can only use
ULPI and serial PHY interfaces.  The patch fixes the wrong
type in dts.

This patch fixes USB malfunctioning on the MPC837xE-RDB boards.

Similar patch has been already applied for the MDS boards:

  commit 28b95885
  Author: Li Yang <leoli@freescale.com>
  Date:   Thu Mar 6 18:42:26 2008 +0800

      [POWERPC] 83xx: Fix wrong USB phy type in mpc837xmds dts

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>