util: reduce debug log in virPCIGetVirtualFunctions()

util: reduce debug log in virPCIGetVirtualFunctions()

Due to debug logs like this:

  virPCIGetDeviceAddressFromSysfsLink:2432 : Attempting to resolve device path from device link '/sys/class/net/eth1/device/virtfn6'
  logStrToLong_ui:2369 : Converted '0000:07:00.7' to unsigned int 0
  logStrToLong_ui:2369 : Converted '07:00.7' to unsigned int 7
  logStrToLong_ui:2369 : Converted '00.7' to unsigned int 0
  logStrToLong_ui:2369 : Converted '7' to unsigned int 7
  virPCIGetDeviceAddressFromSysfs:1947 : virPCIDeviceAddress 0000:07:00.7
  virPCIGetVirtualFunctions:2554 : Found virtual function 7

printed *once for each SR-IOV Virtual Function* of a Physical Function
each time libvirt retrieved the list of VFs (so if the system has 128
VFs, there would be 900 lines of log for each call), the debug logs on
any system with a large number of VFs was dominated by "information"
that was possibly useful for debugging when the code was being
written, but is now useless for debugging of any problem on a running
system, and only serves to obscure the real useful information. This
overkill has no place in production code, so this patch removes it.