PCI: thunder-pem: Use Cavium assigned hardware ID for ThunderX host controller

"CAV" is the only PNP/ACPI hardware ID vendor prefix assigned to Cavium so
fix this as it should be from day one.

Fixes: 44f22bd9

 ("PCI: Add MCFG quirks for Cavium ThunderX pass2.x host controller")
Tested-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Robert Richter <rrichter@cavium.com>
CC: stable@vger.kernel.org	# v4.10+