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)
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passed debian #432223

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  Build+Test
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passed meson-armhf #432231

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passed meson-clang #432225

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passed meson-clover #432229

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passed meson-i386 #432233

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passed meson-main #432228

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passed meson-swr-glvnd #432224

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passed meson-vulkan #432230

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passed scons-llvm #432235

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passed scons-nollvm #432234

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passed scons-swr #432226

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passed scons-win64 #432227

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