[ARM] Fix -Wimplicit-fallthrough warning. NFCI.

llvm-svn: 307480
diff --git a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
index 90f635c..582153d 100644
--- a/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
+++ b/llvm/lib/Target/ARM/ARMAsmPrinter.cpp
@@ -1103,6 +1103,7 @@
     case ARM::tPUSH:
       // Special case here: no src & dst reg, but two extra imp ops.
       StartOp = 2; NumOffset = 2;
+      LLVM_FALLTHROUGH;
     case ARM::STMDB_UPD:
     case ARM::t2STMDB_UPD:
     case ARM::VSTMDDB_UPD: