USB: ffs-test: fix length argument of out function call

The out functions should only handle actual available data instead of the complete buffer.
Otherwise for example the ep0_consume function will report ghost events since it tries to decode
the complete buffer - which may contain partly invalid data.
Signed-off-by: Matthias Fend <matthias.fend@wolfvision.net>
Cc: stable <stable@vger.kernel.org>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/usb/ffs-test.c

@@ -297,7 +297,7 @@ static void *start_thread_helper(void *arg)
 
 		ret = t->in(t, t->buf, t->buf_size);
 		if (ret > 0) {
-			ret = t->out(t, t->buf, t->buf_size);
+			ret = t->out(t, t->buf, ret);
 			name = out_name;
 			op = "write";
 		} else {