[V3] PCI: fu740: Drop to 2.5GT/s to fix initial device probing on some boards

[Maciej W. Rozycki]

Hi Ben,

> >   Any idea what might be causing it?  I can't see it being explicitly set
> > or cleared anywhere, be it in U-Boot or Linux, so it must be done by the
> > device itself depending on something.  And the lack of this capability
> > seems to me like non-compliance for a multiple-lane, multiple-speed
> > device.
> 
> I'll see if we can reproduce this

 Have you been able to look into it?

  Maciej