s390/sysinfo: Remove exception handling from __stsi()

The exception handling for __stsi() was added in 2001 when it still was
possible to run Linux on systems without LPAR hypervisor, and therefore
without an stsi instruction. Given that this is not supported anymore
remove the exception handling from the __stsi() inline assembly.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>