[PATCH] Fix a deadlock in usbtest

ctrl_complete functions acquires ctx->lock and tries to unlink
all queued urbs in case of errors through usb_unlink_urb func.
In its turn usb_unlink_urb calls, through the hcd driver,
usb_hcd_giveback_urb which calls ctrl_complete again. At this
time, ctx->lock is already taken by the same function.

Signed-off-by: Franck Bui-Huu <vagabon.xyz@gmail.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>