PCI: xgene: Fix CRS SV comment

Configuration Request Retry Status ("CRS") must be supported by all PCIe
devices.  CRS Software Visibility is an optional feature that enables a
Root Port to make CRS visible to software by returning a special data value
to complete a config read.

Clarify a comment to say that it is "CRS SV", not "CRS", that can be
enabled.

Link: https://lore.kernel.org/r/20210126213503.2922848-1-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>