ext4: ext4_inode_is_fast_symlink should use EXT4_CLUSTER_SIZE

Can be reproduced by xfstests 62 with bigalloc and 128bit size inode.

Signed-off-by: Yongqiang Yang <yangyongqiang01@baidu.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>