usb: musb: blackfin: remove incorrect __exit_p()

bfin_remove() is not (nor should it be) marked as __exit, so we should
not be using __exit_p() wrapper with it, otherwise unbinding through
sysfs does not work properly.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>