staging: gpib: Change error code for no listener

When doing a write a test is made to see whether there are any
listeners. The code was returning ENODEV which is incorrect.
The user library translates ENOTCONN to a user level no listener
error code.

Change the error code to ENOTCONN.

Fixes: 4cd654f ("staging: gpib: Add gpio bitbang GPIB driver")
Tested-by: Dave Penkler <dpenkler@gmail.com>
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20250418173434.2892-7-dpenkler@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: dpenkler

drivers/staging/gpib/gpio/gpib_bitbang.c

@@ -516,7 +516,7 @@ static int bb_write(struct gpib_board *board, u8 *buffer, size_t length,
 		   gpiod_get_value(NRFD), gpiod_get_value(NDAC));
 
 	if (gpiod_get_value(NRFD) && gpiod_get_value(NDAC)) { /* check for listener */
-		retval = -ENODEV;
+		retval = -ENOTCONN;
 		goto write_end;
 	}