powerpc/pseries/dlpar: Remove unnecessary cast to kfree()

Remove unnecassary cast in the argument to kfree().

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200708072228.30776-1-vulab@iscas.ac.cn