[POWERPC] qe_lib: fix few fluffy negligences

One is intoduced by me (of_node_put() absence) and another was
present already (not checking for NULL).

Found by Stephen Rothwell.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>