usb: musb: tusb: remove dead code

musb_in_tusb() is always set to 0, because CONFIG_USB_TUSB6010 is never
set (it should have been CONFIG_USB_MUSB_TUSB6010). But musb_in_tusb()
is unused anyway, so remove a few lines of dead code.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Felipe Balbi <balbi@ti.com>