kvm: fix typo in flag name

KVM_X86_DISABLE_EXITS_HTL really refers to exit on halt.
Obviously a typo: should be named KVM_X86_DISABLE_EXITS_HLT.

Fixes: caa057a2

 ("KVM: X86: Provide a capability to disable HLT intercepts")
Cc: stable@vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>