thunderbolt: Get rid of usb4_usb3_port_actual_link_rate()

It turns out there is no need to use the actual link rate when
reclaiming bandwidth for USB 3.x. The reason is that we use consumed
bandwidth which is coming from xHCI when releasing bandwidth (for
example for DisplayPort tunneling) and this can be anything between
1000 Mb/s to maximum, so when reclaiming we can just bump it up back to
maximum instead of actual link rate (which is always <= maximum).

This allows us to get rid of couple of unnecessary lines of code.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>