ram: Move last_req_rb to RAMState

It was on MigrationState when it is only used inside ram.c for
postcopy.  Problem is that we need to access it without being able to
pass it RAMState directly.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
diff --git a/migration/ram.c b/migration/ram.c
index 2f5cbd1..cec51b4 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -204,6 +204,8 @@
     QemuMutex bitmap_mutex;
     /* Ram Bitmap protected by RCU */
     RAMBitmap *ram_bitmap;
+    /* The RAMBlock used in the last src_page_requests */
+    RAMBlock *last_req_rb;
 };
 typedef struct RAMState RAMState;
 
@@ -1226,12 +1228,13 @@
                          ram_addr_t start, ram_addr_t len)
 {
     RAMBlock *ramblock;
+    RAMState *rs = &ram_state;
 
     ms->postcopy_requests++;
     rcu_read_lock();
     if (!rbname) {
         /* Reuse last RAMBlock */
-        ramblock = ms->last_req_rb;
+        ramblock = rs->last_req_rb;
 
         if (!ramblock) {
             /*
@@ -1249,7 +1252,7 @@
             error_report("ram_save_queue_pages no block '%s'", rbname);
             goto err;
         }
-        ms->last_req_rb = ramblock;
+        rs->last_req_rb = ramblock;
     }
     trace_ram_save_queue_pages(ramblock->idstr, start, len);
     if (start+len > ramblock->used_length) {