ext4: let ext4_ext_rm_leaf work with EXT_DEBUG defined

The variable 'block' is removed by commit 750c9c47

, so use the
replacement ex_ee_block instead.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>