powerpc/pseries/hotplug-cpu: Remove double free in error path

In the unlikely event that the device tree lacks a /cpus node,
find_dlpar_cpus_to_add() oddly frees the cpu_drcs buffer it has been
passed before returning an error. Its only caller also frees the
buffer on error.

Remove the less conventional kfree() of a caller-supplied buffer from
find_dlpar_cpus_to_add().

Fixes: 90edf184 ("powerpc/pseries: Add CPU dlpar add functionality")
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190919231633.1344-1-nathanl@linux.ibm.com