staging: erofs: fix compression mapping beyond EOF

Logical address of EOF LTP mapping should start at
`inode->i_size' rather than `inode->i_size - 1' to
`m_la(in)', fix it.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>