usb: musb: omap2plus bus glue needs USB host support

The musb/omap2430.c bus glue driver calls usb_hcd_poll_rh_status,
which is only available if CONFIG_USB is also set, i.e. we
are building USB host mode and not just endpoint mode.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Felipe Balbi <balbi@ti.com>