KVM: x86: Remove a spurious export of a static function

A recent change inadvertently exported a static function, which results
in modpost throwing a warning.  Fix it.

Fixes: cbbaa272

 ("KVM: x86: fix presentation of TSX feature in ARCH_CAPABILITIES")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>