CVE-2024-27389 pstore: inode: Only d_invalidate() is needed

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

pstore: inode: Only d_invalidate() is needed

Unloading a modular pstore backend with records in pstorefs would
trigger the dput() double-drop warning:

WARNING: CPU: 0 PID: 2569 at fs/dcache.c:762 dput.part.0+0x3f3/0x410

Using the combo of d_drop()/dput() (as mentioned in
Documentation/filesystems/vfs.rst) isn’t the right approach here, and
leads to the reference counting problem seen above. Use d_invalidate()
and update the code to not bother checking for error codes that can
never happen.