gather throw error on cpu and gpu array inputs

Author: yuehhua

src/gather.jl

@@ -63,3 +63,8 @@ function NNlib.gather!(dst::AnyCuArray, src::AnyCuArray, idx::AnyCuArray)
     kernel(args...; threads=threads, blocks=blocks)
     return dst
 end
+
+function NNlib.gather(src::AnyCuArray, idx::AbstractArray)
+    err_msg = "src and idx both must be on GPU, but received $(typeof(src)) and $(typeof(idx)), respectively."
+    throw(ArgumentError(err_msg))
+end