USB: symbolserial: Correct transferred data size

USB: symbolserial: Correct transferred data size

The scanner (here DS3508) always returns 64 bytes per urb buffer. The first
byte indicates the data length used in the current buffer. There even was
a comment describing this. But the comment also said that we'll send
everything in the buffer to the tty layer. That means sending the actual
barcode data and lots of trailing zeroes. This patch lets the driver only
send the real data.

Signed-off-by: Philipp Hachtmann <hachti@hachti.de>
Acked-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>