[S390] cio: fix sanity checks in ccwgroup driver.

Some sanity checks in the ccw group driver test the output of
container_of macros to be !NULL. Test the input parameters instead.

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