[Fix] Fix type in Swin Transformer (open-mmlab#1274)

Author: MengzhangLI

mmseg/models/backbones/swin.py

@@ -479,7 +479,7 @@ class SwinTransformer(BaseModule):
         embed_dims (int): The feature dimension. Default: 96.
         patch_size (int | tuple[int]): Patch size. Default: 4.
         window_size (int): Window size. Default: 7.
-        mlp_ratio (int): Ratio of mlp hidden dim to embedding dim.
+        mlp_ratio (int | float): Ratio of mlp hidden dim to embedding dim.
             Default: 4.
         depths (tuple[int]): Depths of each Swin Transformer stage.
             Default: (2, 2, 6, 2).
@@ -610,7 +610,7 @@ def __init__(self,
             stage = SwinBlockSequence(
                 embed_dims=in_channels,
                 num_heads=num_heads[i],
-                feedforward_channels=mlp_ratio * in_channels,
+                feedforward_channels=int(mlp_ratio * in_channels),
                 depth=depths[i],
                 window_size=window_size,
                 qkv_bias=qkv_bias,