spirv: Fix order of barriers in SpvOpControlBarrier

Semantically, the memory barrier has to come first to wait
for the completion of pending memory requests.
Afterwards, the workgroups can be synchronized.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
13 jobs for !1383 with barrier in 19 minutes and 55 seconds (queued for 6 seconds)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #432223
debian

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  Build+Test
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meson-arm64

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meson-armhf

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meson-clang

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meson-clover

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passed #432233
meson-i386

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passed #432228
meson-main

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passed #432224
meson-swr-glvnd

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passed #432230
meson-vulkan

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passed #432235
scons-llvm

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scons-nollvm

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scons-swr

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scons-win64

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