IB/sysfs: remove unused va_list args

_show_port_gid_attr performs a va_end on some unused va_list args.
Clean this up by removing the args completely.

Fixes: 470be516

 ("IB/core: Add gid attributes to sysfs")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>