fm10k: update fm10k_slot_warn to use pcie_get_minimum link

fm10k: update fm10k_slot_warn to use pcie_get_minimum link

This is useful in cases where we connect to a slot at Gen3, but the slot
is behind a bus which only connected at Gen2. This generally only
happens when a PCIe switch is in the sequence of devices, and can be
very confusing when you see slow performance with no obvious cause.

I am aware this patch has a few lines that break 80 characters, but
there does not seem to be a readable way to format them to less than 80
characters. Suggestions welcome.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>