[S390] cio: fix chsc_chp_vary

The functions called by chsc_chp_vary operate on pointers to channel
path ids not channel path links. (This worked by chance since the id
is the first member of the link structure)

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>