exec.c: correct the maximum skip value during compact

skip is defined with 6 bits. So the maximum value should be (1 << 6).

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Message-Id: <20190321082555.21118-6-richardw.yang@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

exec.c

@@ -324,7 +324,7 @@ static void phys_page_compact(PhysPageEntry *lp, Node *nodes)
     assert(valid_ptr < P_L2_SIZE);
 
     /* Don't compress if it won't fit in the # of bits we have. */
-    if (lp->skip + p[valid_ptr].skip >= (1 << 3)) {
+    if (lp->skip + p[valid_ptr].skip >= (1 << 6)) {
         return;
     }