USB: usbtest: fix test number in log message

This patch (as1639) fixes a minor bug in the usbtest driver.  Due to
concurrent changes, a test originally written as number 17 got changed
to number 24, but the corresponding change was not made in the log
message.  This updates the log message.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>