ref_tracker: don't use %pK in pr_ostream() output

ref_tracker: don't use %pK in pr_ostream() output

As Thomas Weißschuh points out [1], it is now preferable to use %p
instead of hashed pointers with printk(), since raw pointers should no
longer be leaked into the kernel log. Change the ref_tracker
infrastructure to use %p instead of %pK in its formats.

[1]: https://lore.kernel.org/netdev/20250414-restricted-pointers-net-v1-0-12af0ce46cdd@linutronix.de/

Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20250618-reftrack-dbgfs-v15-1-24fc37ead144@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>