KVM: VMX: use correct vmcs_read/write for guest segment selector/base

commit 96794e4ed4d758272c486e1529e431efb7045265 upstream.

Guest segment selector is 16 bit field and guest segment base is natural
width field. Fix two incorrect invocations accordingly.

Without this patch, build fails when aggressive inlining is used with ICC.

Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>