gfs2: make gfs2_fs_parameters static

The gfs2_fs_parameters is not used outside the unit
it is declared in, so make it static.

Fixes the following sparse warning:

fs/gfs2/ops_fstype.c:1331:39: warning: symbol 'gfs2_fs_parameters' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Andrew Price <anprice@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>