nir: Fix undef creation in loop unrolling

Copy_deref intrinsics don't set the num_components, so we need to
get it from the destination.  Missing this was causing some invalid
NIR being produced from shader-db.

Fixes: e8a8937a "nir: add partial loop unrolling support"
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
21 jobs for !436 with review/nir-fix-loop-unroll in 109 minutes and 24 seconds (queued for 1 minute and 53 seconds)
detached
Status Job ID Name Coverage
  Containers Build
passed #168347
ubuntu

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  Build+Test
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make-gallium-drivers-other

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make-gallium-drivers-radeonsi

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make-gallium-drivers-swr

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make-gallium-st-clover-llvm

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make-gallium-st-clover-llvm-39

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make-gallium-st-other

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make-loader-classic-dri

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make-vulkan

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meson-gallium-clover-llvm

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meson-gallium-clover-llvm39

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meson-gallium-drivers-other

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meson-gallium-radeonsi

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meson-gallium-st-other

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meson-gallium-swr

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meson-glvnd

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meson-loader-classic-dri

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meson-vulkan

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scons-llvm

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scons-nollvm

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scons-swr

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