memory: fix compat handling of XENMEM_access_op

Within compat_memory_op() this needs to be placed in the first switch()
statement, or it ends up being dead code (as that first switch() has a
default case chaining to compat_arch_memory_op()).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Compile tested only.

--- a/xen/common/compat/memory.c
+++ b/xen/common/compat/memory.c
@@ -320,6 +320,11 @@ int compat_memory_op(unsigned int cmd, X
             break;
         }
 
+        case XENMEM_access_op:
+            return mem_access_memop(cmd,
+                                    guest_handle_cast(compat,
+                                                      xen_mem_access_op_t));
+
         case XENMEM_get_vnumainfo:
         {
             enum XLAT_vnuma_topology_info_vdistance vdistance =
@@ -495,10 +500,6 @@ int compat_memory_op(unsigned int cmd, X
             break;
         }
 
-        case XENMEM_access_op:
-            rc = mem_access_memop(cmd, guest_handle_cast(compat, xen_mem_access_op_t));
-            break;
-
         case XENMEM_add_to_physmap_batch:
             start_extent = end_extent;
             break;