staging: gpib: Removing unused function CFGn

Removing CFGn since it is not called by kernel code nor any of the gpib
drivers.

Signed-off-by: Michael Rubin <matchstick@neverthere.org>
Link: https://lore.kernel.org/r/20250417153837.92690-1-matchstick@neverthere.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>