MFC 298950: Fix an off by one error when remapping MSI-X vectors.

MFC 298950: Fix an off by one error when remapping MSI-X vectors.

pci_remap_msix() can be used to alter the mapping of allocated
MSI-X vectors to the MSI-X table.  The code had an off by one error
when adding the IRQ resources after performing a remap.  This was
fatal for any vectors in the table that used the "last" valid IRQ as
those vectors were assigned a garbage IRQ value.

git-svn-id: svn://svn.freebsd.org/base/stable/10@304511 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f