Update to support fp16 training of GFL (#3410)

mmdet/models/dense_heads/gfl_head.py

@@ -52,7 +52,7 @@ class Integral(nn.Module):
                 offsets from the box center in four directions, shape (N, 4).
         """
         x = F.softmax(x.reshape(-1, self.reg_max + 1), dim=1)
-        x = F.linear(x, self.project).reshape(-1, 4)
+        x = F.linear(x, self.project.type_as(x)).reshape(-1, 4)
         return x