[test] Check depthwise conv is vectorized in test (NFC) (#18225)

Quick follow-up to #18190, as I realized the test may also pass if the
conv fails to vectorize.

Signed-off-by: Benjamin Maxwell <benjamin.maxwell@arm.com>
diff --git a/compiler/src/iree/compiler/Codegen/Common/test/generic_vectorization.mlir b/compiler/src/iree/compiler/Codegen/Common/test/generic_vectorization.mlir
index 38e0f5e..54a0669 100644
--- a/compiler/src/iree/compiler/Codegen/Common/test/generic_vectorization.mlir
+++ b/compiler/src/iree/compiler/Codegen/Common/test/generic_vectorization.mlir
@@ -503,3 +503,6 @@
 // CHECK-MASK-LABEL: func.func @depthwise_conv_fold_away_masking
 // CHECK-MASK-NOT: vector.create_mask
 // CHECK-MASK-NOT: vector.constant_mask
+// CHECK-MASK:     vector.fma
+// CHECK-MASK-NOT: vector.create_mask
+// CHECK-MASK-NOT: vector.constant_mask