gfs2: Rename the {freeze,thaw}_super callbacks

[ Upstream commit 097cca52 ]

Rename gfs2_freeze to gfs2_freeze_super and gfs2_unfreeze to
gfs2_thaw_super to match the names of the corresponding super
operations.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Stable-dep-of: f66af88e ("gfs2: Stop using gfs2_make_fs_ro for withdraw")
Signed-off-by: Sasha Levin <sashal@kernel.org>