fix JuliaMath#95

Author: ziyiyin97

ext/AbstractFFTsChainRulesCoreExt.jl

@@ -37,7 +37,7 @@ function ChainRulesCore.rrule(::typeof(rfft), x::AbstractArray{<:Real}, dims)
 
     project_x = ChainRulesCore.ProjectTo(x)
     function rfft_pullback(ȳ)
-        x̄ = project_x(brfft(ChainRulesCore.unthunk(ȳ) ./ scale, d, dims))
+	x̄ = project_x(brfft(ChainRulesCore.unthunk(ȳ) ./ typeof(x)(scale), d, dims))
         return ChainRulesCore.NoTangent(), x̄, ChainRulesCore.NoTangent()
     end
     return y, rfft_pullback