mfd: omap-usb-host: override number of ports from platform data

Both OMAP4 and 5 exhibit the same revision ID in the REVISION register
but they have different number of ports i.e. 2 and 3 respectively.
So we can't rely on REVISION register for number of ports on OMAP5
and depend on platform data (or device tree) instead.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>