libgfs2: combine gfs_inode_read and gfs_inode_get
    
    Functions gfs_inode_read and gfs_inode_get were nearly identical.
    They did the same exact thing, but one operated on a buffer passed in
    while the other read the buffer from the media.  This patch combines
    the two into a common function and two replacement stubs.
    
    rhbz#675723