s390/dma: do not call debug_dma after free

In dma_free_coherent call debug_dma_free_coherent before deallocating
the memory to avoid a possible use after free.

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