qeth: cleanup channel path descriptor function

Cleanup the qeth_get_channel_path_desc function and rename it
to qeth_update_from_chp_desc. No functional change.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Acked-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>