usb: musb: eliminate musb_to_hcd

With the hcd is now a direct member of struct musb, we can now simply
eliminate the musb_to_hcd() macro. There aren't that many users left
anyway, as some where already fixed up when parts were factored out to
musb_host.c

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Felipe Balbi <balbi@ti.com>