kernfs: Move dput() outside of the RCU section.

kernfs: Move dput() outside of the RCU section.

Al Viro pointed out that dput() might sleep and must not be invoked
within an RCU section.

Keep only find_next_ancestor() winthin the RCU section.
Correct the wording in the comment.

Fixes: 6ef5b6fae3040 ("kernfs: Drop kernfs_rwsem while invoking lookup_positive_unlocked().")
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20250221084232.xksA_IQ4@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>