Fixing assert in value liveness of blocks with a single op.

iree/compiler/Dialect/VM/Analysis/ValueLiveness.cpp

diff --git a/iree/compiler/Dialect/VM/Analysis/ValueLiveness.cpp b/iree/compiler/Dialect/VM/Analysis/ValueLiveness.cpp
index f94ac9f..c716d57 100644
--- a/iree/compiler/Dialect/VM/Analysis/ValueLiveness.cpp
+++ b/iree/compiler/Dialect/VM/Analysis/ValueLiveness.cpp
@@ -264,6 +264,7 @@
       Operation *lastUse = &block.front();
       for (auto &use : value.getUses()) {
         if (use.getOwner()->getBlock() != &block) continue;
+        if (lastUse == use.getOwner()) continue;
         if (lastUse->isBeforeInBlock(use.getOwner())) {
           lastUse = use.getOwner();
         }