KVM: x86: wean fast IN from emulator_pio_in

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86: wean fast IN from emulator_pio_in

Use __emulator_pio_in() directly for fast PIO instead of bouncing through

emulator_pio_in() now that __emulator_pio_in() fills "val" when handling

in-kernel PIO. vcpu->arch.pio.count is guaranteed to be '0', so this a

pure nop.

emulator_pio_in_emulated is now the last caller of emulator_pio_in.

No functional change intended.