KVM: x86: complete fast IN directly with complete_emulator_pio_in()

Use complete_emulator_pio_in() directly when completing fast PIO, there's
no need to bounce through emulator_pio_in(): the comment about ECX
changing doesn't apply to fast PIO, which isn't used for string I/O.

No functional change intended.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>