staging: gpib: Change error code for no listener

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: 4cd654f84769 ("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>