[Common] Fix checks in quantize_transpose_vector_blockwise_fp4 (#2299)

fix checks in unoptimized non-rht fp4 quantize kernel
Signed-off-by: Jeremy Berchtold <jberchtold@nvidia.com>

transformer_engine/common/transpose/quantize_transpose_vector_blockwise_fp4.cu

@@ -718,13 +718,11 @@ void quantize_transpose_vector_blockwise_fp4(
   // raise error if pow2_scale is true
   NVTE_CHECK(!pow2_scale, "No support for pow2_scale for MXFP4 for now");
 
-  if (!return_identity && !return_transpose) {
-    return;
-  }
+  NVTE_CHECK(return_identity || return_transpose,
+             "At least one of return_identity or return_transpose must be true.");
 
-  if (use_2d_quantization && !return_identity) {
-    return;
-  }
+  NVTE_CHECK(return_identity || !use_2d_quantization,
+             "2D block quantization is only supported when return_identity is true.");
 
   const size_t row_length = input.shape.size() > 0 ? input.shape.at(input.shape.size() - 1) : 1u;
   size_t num_elements = row_length;
@@ -777,7 +775,7 @@ void quantize_transpose_vector_blockwise_fp4(
       input.dtype, InputType,
 
       TRANSFORMER_ENGINE_TYPE_SWITCH_FP4x2_ONLY(
-          output.dtype, 2, OutputType,
+          return_identity ? output.dtype : output_t.dtype, 2, OutputType,
 
           dim3 grid(num_blocks_x, num_blocks_y, 1);