KVM: PPC: Book3S HV: small pseries_do_hcall cleanup

Functionality should not be changed.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210528090752.3542186-28-npiggin@gmail.com