staging: gpib: Avoid plain integers as NULL pointers

staging: gpib: Avoid plain integers as NULL pointers

A number of drivers were comparing request_region() with 0,
others were passing 0 instead of NULL as a pointer argument.

This led to the following sparse warning, for example:

cb7210/cb7210.c:1043:72: warning: Using plain integer as NULL pointer

Use !request_region() to test for NULL return and use NULL instead
of 0 as pointer parameter.

Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20250114165403.16410-4-dpenkler@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>