LU-10185 gnilnd: treat seq_printf as void function

Starting with the 4.3 linux kernel seq_printf is a void
function not returning the character count. Earlier cleanups
did not update all of gnilnd to accomodate this change
when they updated the rest of Lustre. This change takes
care of what was missed.

Test-parameters: trivial

Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Ie76c1cc7578cb5919a1f2aca6fb15fd8b75882c1
Reviewed-on: https://review.whamcloud.com/29893
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Doug Oucharek <dougso@me.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>