USB: atmel_usb_udc: Use kzalloc() to allocate ep structures

This ensures that all fields are properly initialized.

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>