powerpc/mpc85xx: Correct CONFIG_USB_MAX_CONTROLLER_COUNT for p1025

Correct the value CONFIG_USB_MAX_CONTROLLER_COUNT macro to 1
for p1025 as it has one USB controller

Signed-off-by: Nikhil Badola <nikhil.badola@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>