Revert "usb-linux: remove unreachable default in switch statement"

This reverts commit 3c9c706c3b66d838942aba53c0d3fdcdf06c7423.

This breaks build (gcc 4.3.2):
    CC    usb-linux.o
 cc1: warnings being treated as errors
 /src/qemu/usb-linux.c: In function 'usb_linux_update_endp_table':
 /src/qemu/usb-linux.c:759: error: 'type' may be used uninitialized in
 this function

Reported-by: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
