migration/postcopy: the valid condition is one less then end

If one equals end, it means we have gone through the whole bitmap.

Use a more restrict check to skip a unnecessary condition.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Message-Id: <20190627020822.15485-2-richardw.yang@linux.intel.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/ram.c

@@ -2865,7 +2865,7 @@ static int postcopy_send_discard_bm_ram(MigrationState *ms,
     for (current = 0; current < end; ) {
         unsigned long one = find_next_bit(unsentmap, end, current);
 
-        if (one <= end) {
+        if (one < end) {
             unsigned long zero = find_next_zero_bit(unsentmap, end, one + 1);
             unsigned long discard_length;