KVM: x86.c make kvm_load_realmode_segment static

Noticed by sparse:
arch/x86/kvm/x86.c:3591:5: warning: symbol 'kvm_load_realmode_segment' was not declared. Should it be static?

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>