powerpc/p1_p2_rdb_pc: Fix endian access issue on EHCI intinalization

This issue is exposed after commit 9000eddb ("drivers/usb/ehci:
Use platform-specific accessors"), the wrong endianness of EHCI
controller programing will cause USB function down.

Signed-off-by: Ran Wang <ran.wang_1@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>