Add block check calls to the read_block validate functions.  This is the
almost all of the read-side checking of metaecc.  xattr buckets are not checked
yet.   Writes are also unchecked, and so a read-write mount will quickly fail.
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>