i386/msi: Correct mask of destination ID in MSI address

i386/msi: Correct mask of destination ID in MSI address

According to SDM 10.11.1, only [19:12] bits of MSI address are
Destination ID, change the mask to avoid ambiguity for VT-d spec
has used the bit 4 to indicate a remappable interrupt request.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>