thunderbolt: Do not allow subtracting more NFC credits than configured

thunderbolt: Do not allow subtracting more NFC credits than configured

BugLink: https://bugs.launchpad.net/bugs/1955016
This might happen if the boot firmware uses different amount of NFC
credits than what the router suggests, or we are dealing with pre-USB4
device.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
(cherry picked from commit 6cb27a04fb779717c4a3d20233b93596885838cf)
Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>