usb.c

While debugging some USB stuff, I've first missed that there are actually
two defines necessary to get usefull output. The one needed to get debug output
for the communication with HUBs was burried somewhere deep inside the code.

Change that so that a #define DEBUG is enough while still leaving the possibility
to reduce unwanted debug output.

Signed-off-by: Alexander Holler <holler@ahsoftware.de>