USB: serial: ti_usb_3410_5052: fix control-message error handling

commit 39712e8bfa8d3aa6ce1e60fc9d62c9b076c17a30 upstream.

Make sure to detect and return an error on zero-length control-message
transfers when reading from the device.

This addresses a potential failure to detect an empty transmit buffer
during close.

Also remove a redundant check for short transfer when sending a command.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>