gfs2: Avoid access time thrashing in gfs2_inode_lookup

In gfs2_inode_lookup, we initialize inode->i_atime to the lowest
possibly value after gfs2_inode_refresh may already have been called.
This should be the other way around, but we didn't notice because
usually the inode type is known from the directory entry and so
gfs2_inode_lookup won't call gfs2_inode_refresh.

In addition, only initialize ip->i_no_formal_ino from no_formal_ino when
actually needed.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>