ntfs: sanitize MFT references returned from ntfs_lookup_inode_by_name()

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

ntfs: sanitize MFT references returned from ntfs_lookup_inode_by_name()

ntfs_lookup_inode_by_name() returns MFT references read from directory
index entries on disk. These values are untrusted, but the function can
currently return an error-marked MFT reference to its callers without
validating it.

Callers later decode lookup failures with MREF_ERR(). A crafted NTFS image
can set the MREF error bit while leaving the low bits as an arbitrary
value, causing callers to consume a bogus pseudo-errno instead of treating
the lookup result as corrupted on-disk metadata.

Fix this at the source by normalizing every error-marked MFT reference
returned from ntfs_lookup_inode_by_name() to ERR_MREF(-EIO). Apply this to
all four directory lookup return paths so every caller gets a validated
result without needing additional checks or an API change.

This keeps the sanitization in the common lookup helper, which is cleaner
than duplicating validation in each caller.