ppc/spapr: Fix MAX_CPUS to 255

MAX_CPUS 256 is inconsistent with qemu supporting upto 255 cpus. This
MAX_CPUS number was percolated back to "virsh capabilities" with wrong
max_cpus.
Signed-off-by: NNikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/ppc/spapr.c

@@ -81,7 +81,7 @@
 
 #define TIMEBASE_FREQ           512000000ULL
 
-#define MAX_CPUS                256
+#define MAX_CPUS                255
 
 #define PHANDLE_XICP            0x00001111