atmel_usba: Kill copy_to_fifo() and copy_from_fifo()

These functions do exactly the same as memcpy_toio() and
memcpy_fromio() respectively.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>