tools: Fix memset(&p,0,sizeof(p)) idiom in several places.

gcc 4.8 identifies several places where code of the form memset(x, 0,
sizeof(x)); is used incorrectly, meaning that less memory is set to
zero than required.

Signed-off-by: Michael Young <m.a.young@durham.ac.uk>
Committed-by: Keir Fraser <keir@xen.org>

tools/debugger/kdd/kdd-xen.c

@@ -333,7 +333,7 @@ int kdd_get_regs(kdd_guest *g, int cpuid, kdd_regs *r, int w64)
     if (!cpu) 
         return -1;
 
-    memset(r, 0, sizeof(r));
+    memset(r, 0, sizeof(*r));
     
     if (w64)
         kdd_get_regs_x86_64(cpu, &r->r64);