s390/cio: Fix cleanup of pfn_array alloc failure

If pfn_array_alloc fails somehow, we need to release the pfn_array_table
that was malloc'd earlier.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Message-Id: <20181109023937.96105-2-farman@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>