Fixes the below build warning when driver is built-in.

drivers/mfd/omap-usb-host.c:750:12: warning:
‘usbhs_omap_remove’ defined but not used [-Wunused-function]
Signed-off-by: NRoger Quadros <rogerq@ti.com>
Reviewed-by: NFelipe Balbi <balbi@ti.com>