ext4: Remove unneeded BUG_ON() in ext4_move_extents()

The ext4_move_extents() functions checks with BUG_ON() whether the
exchanged blocks count accords with request blocks count.  But, if the
target range (orig_start + len) includes sparse block(s), 'moved_len'
(exchanged blocks count) does not agree with 'len' (request blocks
count), since sparse block is not counted in 'moved_len'.  This causes
us to hit the BUG_ON(), even though the function succeeded.
Signed-off-by: NAkira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/move_extent.c

@@ -1322,8 +1322,5 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
 	if (ret)
 		return ret;
 
-	/* All of the specified blocks must be exchanged in succeed */
-	BUG_ON(*moved_len != len);
-
 	return 0;
 }