fs/9p: Revert "fs/9p: fix dups even in uncached mode"

This reverts commit be57855f

.

It caused a regression involving duplicate inode numbers in
some tester trees.  The bad behavior seems to be dependent on inode
reuse policy in underlying file system, so it did not trigger in my
test setup.

Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>