GFS2: Fix address space from page function

Now that rgrps use the address space which is part of the super
block, we need to update gfs2_mapping2sbd() to take account of
that. The only way to do that easily is to use a different set
of address_space_operations for rgrps.

Reported-by: Abhi Das <adas@redhat.com>
Tested-by: Abhi Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --cc fs/gfs2/meta_io.c
Simple merge

diff --cc fs/gfs2/meta_io.h
Simple merge

diff --cc fs/gfs2/ops_fstype.c
Simple merge