fix bug in resnet plugin when two plugins are used (#7797)

Author: chhluo

mmdet/models/backbones/resnet.py

@@ -242,7 +242,7 @@ def make_block_plugins(self, in_channels, plugins):
     def forward_plugin(self, x, plugin_names):
         out = x
         for name in plugin_names:
-            out = getattr(self, name)(x)
+            out = getattr(self, name)(out)
         return out
 
     @property