Add generic_mul!

[michel2323]

Fixes: #637

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diff --git a/src/host/linalg.jl b/src/host/linalg.jl
index bc910be..8f55ecd 100644
--- a/src/host/linalg.jl
+++ b/src/host/linalg.jl
@@ -745,7 +745,7 @@ function LinearAlgebra.rotate!(x::AbstractGPUArray, y::AbstractGPUArray, c::Numb
         @inbounds xi = x[i]
         @inbounds yi = y[i]
         @inbounds x[i] = s*yi +      c *xi
-        @inbounds y[i] = c*yi - conj(s)*xi
+        @inbounds y[i] = c * yi - conj(s) * xi
     end
     rotate_kernel!(get_backend(x))(x, y, c, s; ndrange = size(x))
     return x, y