vulkan/metal: fix a typo preventing non-array struct field uniforms from working.

src/modules/graphics/metal/Shader.mm

@@ -298,7 +298,7 @@ void Shader::buildLocalUniforms(const spirv_cross::CompilerMSL &msl, const spirv
 				}
 				else
 				{
-					std::string structname = name = ".";
+					std::string structname = name + ".";
 					buildLocalUniforms(msl, membertype, offset, structname);
 				}
 				continue;

src/modules/graphics/vulkan/Shader.cpp

@@ -427,7 +427,7 @@ void Shader::buildLocalUniforms(spirv_cross::Compiler &comp, const spirv_cross::
 			}
 			else
 			{
-				std::string structname = name = ".";
+				std::string structname = name + ".";
 				buildLocalUniforms(comp, memberType, offset, structname);
 			}
 			continue;