Fix blindspot in per-channelness checking logic of custom grad function

Signed-off-by: Kyunggeun Lee <quic_kyunggeu@quicinc.com>

TrainingExtensions/torch/src/python/aimet_torch/quantsim_straight_through_grad.py

@@ -259,14 +259,14 @@ def asymmetric_gradients(tensor: torch.Tensor,
     grad_offset = grad_xq * (1 - mask_tensor)
 
     dim = list(range(len(tensor.shape)))
-    if len(delta.shape) > 1 and len(tensor.shape) > 1:
+    if delta.numel() > 1 and len(tensor.shape) > 1:
         dim.pop(channel_axis)
 
     num_steps = intermediate_result.num_steps
     encoding_min = intermediate_result.encoding_min
     encoding_max = intermediate_result.encoding_max
 
-    if len(delta.shape) > 1 and len(tensor.shape) == 1:
+    if delta.numel() > 1 and len(tensor.shape) == 1:
         # NOTE: Handle when applying per-channel quant to 1-D Tensor case such as bias tensor in Conv or beta/gamma in BatchNorm
         intermediate_term1 = grad_scale / num_steps
         intermediate_term2 = num_steps / (encoding_max - encoding_min) ** 2 * grad_offset
@@ -301,13 +301,13 @@ def symmetric_gradients(tensor: torch.Tensor,
     mask_tensor = Variable(mask_tensor.type_as(grad.data))
 
     dim = list(range(len(tensor.shape)))
-    if len(delta.shape) > 1 and len(tensor.shape) > 1:
+    if delta.numel() > 1 and len(tensor.shape) > 1:
         dim.pop(channel_axis)
 
     num_steps = intermediate_result.num_steps
     grad_tensor = mask_tensor * grad
 
-    if len(delta.shape) > 1 and len(tensor.shape) == 1:
+    if delta.numel() > 1 and len(tensor.shape) == 1:
         # NOTE: Handle when applying per-channel quant to 1-D Tensor case such as bias tensor in Conv or beta/gamma in BatchNorm
         grad_encoding_max = ((x_quant + offset) * grad) - (mask_tensor * (tensor / delta) * grad)
     else: