[Fix] Fix the calculation error of out_w in MaskedConv2dFunction (#2264)

* [Fix] Fix two intergers can not use / operator in torch1.6

* should not use kernel_h when calculates out_w

mmcv/ops/masked_conv.py

@@ -47,11 +47,13 @@ class MaskedConv2dFunction(Function):
 
         batch_size = features.size(0)
         out_h = int(
-            math.floor((features.size(2) + 2 * pad_h -
-                        (kernel_h - 1) - 1) / stride_h + 1))
+            math.floor(
+                torch.true_divide((features.size(2) + 2 * pad_h -
+                                   (kernel_h - 1) - 1), stride_h) + 1))
         out_w = int(
-            math.floor((features.size(3) + 2 * pad_w -
-                        (kernel_h - 1) - 1) / stride_w + 1))
+            math.floor(
+                torch.true_divide((features.size(3) + 2 * pad_w -
+                                   (kernel_w - 1) - 1), stride_w) + 1))
         mask_inds = torch.nonzero(mask[0] > 0, as_tuple=False)
         output = features.new_zeros(batch_size, out_channel, out_h, out_w)
         if mask_inds.numel() > 0: