erofs: support large folios in inode_share mode

erofs_fill_inode() calls mapping_set_large_folios() on each erofs
file's own mapping, but in inode_share mode reads are routed to the
shared inode's page cache instead, whose mapping never had large
folio support enabled.

Set up large folios for the shared inode's mapping as well.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <xiang@kernel.org>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <xiang@kernel.org>