[D3D12] Fix syntax warnings reported by Clang

src/xenia/gpu/d3d12/d3d12_primitive_processor.cc

@@ -156,7 +156,7 @@ void* D3D12PrimitiveProcessor::RequestHostConvertedIndexBufferForCurrentFrame(
           (coalign_for_simd ? XE_GPU_PRIMITIVE_PROCESSOR_SIMD_SIZE : 0),
       index_size, nullptr, nullptr, &gpu_address);
   if (!mapping) {
-    return false;
+    return nullptr;
   }
   if (coalign_for_simd) {
     ptrdiff_t coalignment_offset =

src/xenia/gpu/d3d12/pipeline_cache.h

@@ -70,12 +70,11 @@ class PipelineCache {
 
   // Retrieves the shader modification for the current state. The shader must
   // have microcode analyzed.
-  DxbcShaderTranslator::Modification
-  PipelineCache::GetCurrentVertexShaderModification(
+  DxbcShaderTranslator::Modification GetCurrentVertexShaderModification(
       const Shader& shader,
       Shader::HostVertexShaderType host_vertex_shader_type) const;
-  DxbcShaderTranslator::Modification
-  PipelineCache::GetCurrentPixelShaderModification(const Shader& shader) const;
+  DxbcShaderTranslator::Modification GetCurrentPixelShaderModification(
+      const Shader& shader) const;
 
   // If draw_util::IsRasterizationPotentiallyDone is false, the pixel shader
   // MUST be made nullptr BEFORE calling this!