[spirv-reader] Fix labels in CFG tests

Bug: tint:3
Change-Id: I13c67649d7e630828eeae34a2b4cd5612d5f2217
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/20420
Reviewed-by: David Neto <dneto@google.com>
diff --git a/src/reader/spirv/function_cfg_test.cc b/src/reader/spirv/function_cfg_test.cc
index 295f1bf..d3f1555 100644
--- a/src/reader/spirv/function_cfg_test.cc
+++ b/src/reader/spirv/function_cfg_test.cc
@@ -576,7 +576,7 @@
 
      %10 = OpLabel
      OpSelectionMerge %99 None
-     OpBranch %30
+     OpBranch %20
 
      %20 = OpLabel
      OpBranch %99
@@ -606,6 +606,9 @@
      OpSwitch %selector %99 30 %30
 
      %30 = OpLabel
+     OpBranch %99
+
+     %40 = OpLabel
      OpBranch %20
 
      %99 = OpLabel