s390/smp: use physical address for SIGP_SET_PREFIX command

Signal processor SIGP_SET_PREFIX command expects physical
address of the lowcore to be installed, but instead the
virtual address is provided.

Note: this does not fix a bug currently, since virtual and
physical addresses are identical.
Reviewed-by: NHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: NAlexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/smp.c

@@ -213,7 +213,7 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
 	if (nmi_alloc_mcesa(&lc->mcesad))
 		goto out;
 	lowcore_ptr[cpu] = lc;
-	pcpu_sigp_retry(pcpu, SIGP_SET_PREFIX, (u32)(unsigned long) lc);
+	pcpu_sigp_retry(pcpu, SIGP_SET_PREFIX, __pa(lc));
 	return 0;
 
 out: