grad filter fixup

Author: MikeInnes

src/nnpack/interface.jl

@@ -89,5 +89,6 @@ end
 function ∇conv_filter!(dw::A, dy::A, x::A, w::A; pad = 0, stride = 1, dilation = 1, algo = UInt32(0), flipkernel = 0) where A<:AbstractArray{Float32, 4}
     flipkernel == 0 && (w = flipweight(w))
     nnp_convolution_kernel_gradient(dw, x, dy, w, padding = pad, stride = stride, algo = algo)
-    flipkernel == 0 ? flipweight(dw) : dw
+    flipkernel && (dw .= flipkernel(dw))
+    return dw
 end