[S390] cio: fix stsch_reset.

Copy inline assembly of stsch and add "memory" to clobber list in order
to prevent gcc from optimizing away the checking of the global variable
"pgm_check_occured".

Signed-off-by: Michael Holzheu <holzheu@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>