[Hexagon] Fix some more -Wimplicit-fallthrough warnings. NFCI.

llvm-svn: 307395
diff --git a/llvm/lib/Target/Hexagon/HexagonSplitDouble.cpp b/llvm/lib/Target/Hexagon/HexagonSplitDouble.cpp
index db268b7..4fa929a 100644
--- a/llvm/lib/Target/Hexagon/HexagonSplitDouble.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonSplitDouble.cpp
@@ -350,6 +350,8 @@
                        MI->getOperand(2).getImm());
     case Hexagon::A4_combineri:
       ImmX++;
+      // Fall through into A4_combineir.
+      LLVM_FALLTHROUGH;
     case Hexagon::A4_combineir: {
       ImmX++;
       int64_t V = MI->getOperand(ImmX).getImm();