powerpc-km82xx.c: replace of_node_put() with __free

The use of the __free macro allows the cleanup to be based on scope
instead of on another function called later. This makes the cleanup
automatic and less susceptible to errors later.

Signed-off-by: David Hunter <david.hunter.linux@gmail.com>
[mpe: Fix over-long line & change log wording]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20240709143553.117053-1-david.hunter.linux@gmail.com