PCI/RCEC: Fix RCiEP device to RCEC association

rcec_assoc_rciep() used "rciep->devfn" (a single byte encoding both the
device and function number) as the device number to check whether the
corresponding bit was set in the RCEC's Association Bitmap for RCiEPs.

But per PCIe r5.0, sec 7.9.10.2, "Association Bitmap for RCiEPs", the
32-bit bitmap contains one bit per device.  That bit applies to all
functions of the device.

Fix rcec_assoc_rciep() to convert the value of "rciep->devfn" to a device
number to ensure that RCiEP devices are correctly associated with the RCEC.

Reported-and-tested-by: Wen Jin <wen.jin@intel.com>
Fixes: 507b460f ("PCI/ERR: Add pcie_link_rcec() to associate RCiEPs")
Link: https://lore.kernel.org/r/20210222011717.43266-1-qiuxu.zhuo@intel.com


Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Sean V Kelley <sean.v.kelley@intel.com>