PCI: don't enable too much HT MSI mapping

Impact: fix bug

Prakash reported that his c51-mcp51 system ondie sound card doesn't work
MSI but if he hack out the HT-MSI on mcp51, the MSI will work well with
sound card.

This patch reworks nv_msi_ht_cap_quirk() and will only avoid enabling
ht_msi on devices following that root device.

Reported-by: Prakash Punnoor <prakash@punnoor.de>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>