staging: gpib: fix uninitialized variable in usb_gpib_command()

staging: gpib: fix uninitialized variable in usb_gpib_command()

The number of bytes written is supposed to be zero at the start of this
function but only one caller, ibcmd(), initializes it to zero.  For the
other three callers, setup_serial_poll(), read_serial_poll_byte() and
cleanup_serial_poll(), it's an uninitialized variable.

Fixes: fce79512a96a ("staging: gpib: Add LPVO DIY USB GPIB driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/a7fed100-ea4d-4dd8-97c6-3fbd2c15f795@stanley.mountain
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>