erofs: get rid of kaddr in `struct z_erofs_maprecorder`

`kaddr` becomes useless after switching to metabuf.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241010235830.1535616-1-hsiangkao@linux.alibaba.com