graphics/libplacebo: unbreak GLSLANG=on after 51a9ba187752

../src/glsl/glslang.cc:213:21: error: excess elements in scalar initializer

/* .limits = */ {
                ^

../src/glsl/glslang.cc:224:1: warning: missing field 'maxMeshWorkGroupSizeX_EXT' initializer [-Wmissing-field-initializers]
};
^
1 warning and 1 error generated.