Documentation: virtual: kvm: correct one bit description in APF case

When commit 6adba527 (KVM: Let host know whether the guest can
handle async PF in non-userspace context.) is introduced, actually
bit 2 still is reserved and should be zero. Instead, bit 1 is 1 to
indicate if asynchronous page faults can be injected when vcpu is
in cpl == 0, and also please see this,

in the file kvm_para.h, #define KVM_ASYNC_PF_SEND_ALWAYS (1 << 1).
Signed-off-by: NTiejun Chen <tiejun.chen@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Documentation/virtual/kvm/msr.txt

@@ -168,7 +168,7 @@ MSR_KVM_ASYNC_PF_EN: 0x4b564d02
 	64 byte memory area which must be in guest RAM and must be
 	zeroed. Bits 5-2 are reserved and should be zero. Bit 0 is 1
 	when asynchronous page faults are enabled on the vcpu 0 when
-	disabled. Bit 2 is 1 if asynchronous page faults can be injected
+	disabled. Bit 1 is 1 if asynchronous page faults can be injected
 	when vcpu is in cpl == 0.
 
 	First 4 byte of 64 byte memory location will be written to by