[libcxx] fix `>> 42` UB in <experimental/simd>

llvm-svn: 338325
diff --git a/libcxx/test/std/experimental/simd/simd.access/default.pass.cpp b/libcxx/test/std/experimental/simd/simd.access/default.pass.cpp
index 697035b..6ce32ca 100644
--- a/libcxx/test/std/experimental/simd/simd.access/default.pass.cpp
+++ b/libcxx/test/std/experimental/simd/simd.access/default.pass.cpp
@@ -161,7 +161,7 @@
     }
     {
       auto c = a;
-      (void)(a[0] + (c[0] >>= a[0]));
+      (void)(a[0] + (c[0] >>= b[0]));
     }
     {
       auto c = a;