Specialize Ref{<:Type} for GPU compatibility.

[maleadt]

Fixes #261. cc @DhairyaLGandhi

[codecov]

Codecov Report

Merging #1109 (a0f3ab5) into master (e0d5b69) will increase coverage by 0.28%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master    #1109      +/-   ##
==========================================
+ Coverage   79.33%   79.61%   +0.28%     
==========================================
  Files         118      118              
  Lines        7915     7889      -26     
==========================================
+ Hits         6279     6281       +2     
+ Misses       1636     1608      -28     

Impacted Files	Coverage Δ
src/compiler/execution.jl	84.44% <50.00%> (-0.31%)	⬇️
lib/cublas/wrappers.jl	90.92% <0.00%> (+0.10%)	⬆️
src/pool.jl	76.52% <0.00%> (+0.33%)	⬆️
lib/curand/random.jl	93.18% <0.00%> (+1.04%)	⬆️
lib/cudadrv/module/jit.jl	69.09% <0.00%> (+1.23%)	⬆️
lib/cudadrv/context.jl	73.50% <0.00%> (+1.23%)	⬆️
src/array.jl	92.19% <0.00%> (+1.28%)	⬆️
src/state.jl	78.44% <0.00%> (+1.83%)	⬆️
lib/cublas/util.jl	84.09% <0.00%> (+1.86%)	⬆️
lib/cudadrv/error.jl	83.33% <0.00%> (+1.93%)	⬆️
... and 7 more

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