erofs: handle 48-bit blocks_hi for compressed inodes

erofs: handle 48-bit blocks_hi for compressed inodes

Combine i_nb.blocks_hi with i_u.blocks_lo when computing
inode->i_blocks for compressed inodes, mirroring the startblk_hi
handling for unencoded inodes a few lines above.  Also evaluate
the shift in u64 to avoid truncation.

Fixes: efb2aef569b3 ("erofs: add encoded extent on-disk definition")
Fixes: 1d191b4ca51d ("erofs: implement encoded extent metadata")
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>