Initialize desc_before_addr, otherwise the USB core won't send the
first 64B Get Device Descriptor request in common/usb.c function
usb_setup_descriptor() . There are some USB devices which expect
this sequence and otherwise can misbehave.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Tom Rini <trini@konsulko.com>