gfs2: Move gfs2_trans_add_databufs

[ Upstream commit d50a64e3 ]

Move gfs2_trans_add_databufs() to trans.c.  Pass in a glock instead of
a gfs2_inode.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Stable-dep-of: 5a90f8d4 ("gfs2: Don't start unnecessary transactions during log flush")
Signed-off-by: Sasha Levin <sashal@kernel.org>