[Eager] Remove elementwise add in conv (#41515)

* remove elementwise add in conv

* use reshape

python/paddle/nn/functional/conv.py

@@ -127,8 +127,12 @@ def _conv_nd(x,
             x, weight, stride, padding, padding_algorithm, groups, dilation,
             data_format, False, -1, False)
         if bias is not None:
-            out = nn.elementwise_add(pre_bias, bias, axis=channel_dim)
-            return out
+            channel_dim = channel_dim + len(
+                x.shape) if channel_dim < 0 else channel_dim
+            tmp_bias = _C_ops.final_state_reshape(
+                bias, bias.shape +
+                [1 for i in range(len(x.shape) - channel_dim - 1)])
+            return _C_ops.final_state_add(pre_bias, tmp_bias)
         else:
             return pre_bias
     if in_dynamic_mode():