s3/vfs: gpfs: adapt vfs_gpfs_is_offline() to changes from 3031815f982e365be50148564d4...

s3/vfs: gpfs: adapt vfs_gpfs_is_offline() to changes from 3031815f982e365be50148564d47d7d5afab46e0

The patchset `git log -2 3031815f982e365be50148564d47d7d5afab46e0`
missed a change to vfs_gpfs_is_offline() which is now merely a helper
function that returns true or false and mustn't call into the VFS.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>
Autobuild-User(master): David Disseldorp <ddiss@samba.org>
Autobuild-Date(master): Mon Oct 17 21:28:12 CEST 2016 on sn-devel-144