KVM: x86: Directly query supported PERF_CAPABILITIES for WRMSR checks

Use kvm_caps.supported_perf_cap directly instead of bouncing through
kvm_get_msr_feature() when checking the incoming value for writes to
PERF_CAPABILITIES.

Note, kvm_get_msr_feature() is guaranteed to succeed when getting
PERF_CAPABILITIES, i.e. dropping that check is a nop.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221006000314.73240-9-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>