gsdx: c_str() is useless when parameter is a string

Reported by clang tidy

plugins/GSdx/GSRenderer.cpp

@@ -69,7 +69,7 @@ GSRenderer::~GSRenderer()
 
 bool GSRenderer::CreateWnd(const string& title, int w, int h)
 {
-	return m_wnd->Create(title.c_str(), w, h);
+	return m_wnd->Create(title, w, h);
 }
 
 bool GSRenderer::CreateDevice(GSDevice* dev)

plugins/GSdx/GSTextureCacheSW.cpp

@@ -370,7 +370,7 @@ bool GSTextureCacheSW::Texture::Save(const string& fn, bool dds) const
 
 		t.Unmap();
 
-		return t.Save(fn.c_str());
+		return t.Save(fn);
 	}
 
 	return false;