s390/qdio: add statistics helper macro

qperf_inc() takes a queue as input, but actually updates the statistics
in its qdio_irq parent.
In some contexts we already have access to the qdio_irq struct, and can
avoid the additional dereference.

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>