ceph: remove redundant io_iter_advance()

ceph_sync_read and generic_file_read_iter() have already advanced the
IO iterator.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

fs/ceph/file.c

@@ -835,7 +835,6 @@ again:
 			     ", reading more\n", iocb->ki_pos,
 			     inode->i_size);
 
-			iov_iter_advance(to, ret);
 			read += ret;
 			len -= ret;
 			checkeof = 0;