USB: unaligned problem

The data structure usb_endpoint_descriptor contains an aligned field
wMaxPacketSize, however because it is declared as packed and not ending
on a 16-bit boundary an array of usb_endpoint_descriptor will be
un-aligned.

One example of this is the usb_interface struct's ep_desc field.

Signed-off-by: Daniel Hellstrom <daniel@gaisler.com>