ieee1394: limit early node speed to host interface speed

The following patch limits the node speed to the host interface speed,
before using it.

Signed-off-by: Philippe De Muyter <phdm@macqel.be>

It should actually suffice to do this only for the local node's
speedcap[].  But there is another bug in the speed calculation:
The local node's speed is not correctly propagated to the speeds
which are to be used to access remote nodes.
http://thread.gmane.org/gmane.linux.kernel.firewire.devel/11772/focus=12024



Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>