s390/qeth: reduce hard-coded access to ccw channels

s390/qeth: reduce hard-coded access to ccw channels

BugLink: https://bugs.launchpad.net/bugs/1797367
Where possible use accessor macros and local pointers to access the ccw
channels. This makes it less likely to miss a spot.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 750b162598ec5b65cdb44d18f050b45cb7f8d31b)
Signed-off-by: Frank Heimes <frank.heimes@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>