ISCSI: change num_blocks to 64-bit

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/block/iscsi.c b/block/iscsi.c
index db41bb7..9cd258f 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -38,7 +38,7 @@
     struct iscsi_context *iscsi;
     int lun;
     int block_size;
-    unsigned long num_blocks;
+    uint64_t num_blocks;
     int events;
 } IscsiLun;