Documentation: usb: update usb-tools repository address

It seems that gitorious repository is no longer accessible, so we
replace it with address to active repository.

Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

Documentation/usb/gadget-testing.txt

@@ -434,7 +434,7 @@ On host: serialc -v <vendorID> -p <productID> -i<interface#> -a1 -s1024 \
 
 where seriald and serialc are Felipe's utilities found here:
 
-https://git.gitorious.org/usb/usb-tools.git master
+https://github.com/felipebalbi/usb-tools.git master
 
 12. PHONET function
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