KVM: arm64: Fix Function ID typo for PTP_KVM service

Per include/linux/arm-smccc.h, the Function ID of PTP_KVM service is
defined as ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID. Fix the typo in
documentation to keep the git grep consistent.
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210417113804.1992-1-yuzenghui@huawei.com

Documentation/virt/kvm/arm/ptp_kvm.rst

@@ -7,11 +7,11 @@ PTP_KVM is used for high precision time sync between host and guests.
 It relies on transferring the wall clock and counter value from the
 host to the guest using a KVM-specific hypercall.
 
-* ARM_SMCCC_HYP_KVM_PTP_FUNC_ID: 0x86000001
+* ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID: 0x86000001
 
 This hypercall uses the SMC32/HVC32 calling convention:
 
-ARM_SMCCC_HYP_KVM_PTP_FUNC_ID
+ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID
     ==============    ========    =====================================
     Function ID:      (uint32)    0x86000001
     Arguments:        (uint32)    KVM_PTP_VIRT_COUNTER(0)