nilfs2: propagate directory read errors from nilfs_find_entry()

In the Linux kernel, the following vulnerability has been resolved:

nilfs2: propagate directory read errors from nilfs_find_entry()

Syzbot reported that a task hang occurs in vcs_open() during a fuzzing

test for nilfs2.

The root cause of this problem is that in nilfs_find_entry(), which

searches for directory entries, ignores errors when loading a directory

page/folio via nilfs_get_folio() fails.

If the filesystem images is corrupted, and the i_size of the directory

inode is large, and the directory page/folio is successfully read but

fails the sanity check, for example when it is zero-filled,

nilfs_check_folio() may continue to spit out error messages in bursts.

Fix this issue by propagating the error to the callers when loading a

page/folio fails in nilfs_find_entry().

The current interface of nilfs_find_entry() and its callers is outdated

and cannot propagate error codes such as -EIO and -ENOMEM returned via

nilfs_find_entry(), so fix it together.