lib: s390x: Fix PSW constant

Somehow the ";" got into that patch and now complicates compilation.
Let's remove it and put the constant in braces.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>