s390/qdio: sanitize put_indicator

qdio maintains an array of struct indicator_t. put_indicator takes a pointer
to a member of a struct indicator_t within that array, calculates the index,
and uses the array and the index to get the struct indicator_t.

Simply use the pointer directly.

Although the pointer happens to point to the first member of that struct
use the container_of macro.

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