[GFS2] Change argument of gfs2_dinode_out

Everywhere this was called, a struct gfs2_inode was available,
but despite that, it was always called with a struct gfs2_dinode
as an argument. By making this change it paves the way to start
eliminating fields duplicated between the kernel's struct inode
and the struct gfs2_dinode.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>