Udev rules: replace deprecated $tempnode with $devnode

The $tempnode substitution is so old that it's not even mentioned in the
man page anymore. It is still technically supported by udev, but with
plenty of "deprecated" comments surrounding it.

The preferred modern equivalent of $tempnode is $devnode (or
alternatively, %N).

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Signed-off-by: Justin Gottula <justin@jgottula.com>
Closes #12302