PCI: Do not run NVidia quirks related to MSI with MSI disabled

There is no reason to run NVidia-specific quirks related to HT MSI
mappings with MSI disabled via pci=nomsi, so make
__nv_msi_ht_cap_quirk() return immediately in that case.

This allows at least one machine to boot 100% of the time with
pci=nomsi (it still doesn't boot reliably without that).

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=16443

 .

Cc: stable@kernel.org
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>