Misc: Clean up warnings.

Wsign-compare, Wunused-variable, Wunused-variable.

pcsx2/CDVD/CDVD.cpp

@@ -515,7 +515,7 @@ void cdvdReloadElfInfo(std::string elfoverride)
 		// Recognized and PS2 (BOOT2).  Good job, user.
 		_reloadElfInfo(std::move(elfpath));
 	}
-	catch (Exception::FileNotFound& e)
+	catch ([[maybe_unused]] Exception::FileNotFound& e)
 	{
 #ifdef PCSX2_CORE
 		Console.Error("Failed to load ELF info");

pcsx2/Frontend/VulkanHostDisplay.cpp

@@ -128,7 +128,7 @@ bool VulkanHostDisplay::ChangeRenderWindow(const WindowInfo& new_wi)
 
 void VulkanHostDisplay::ResizeRenderWindow(s32 new_window_width, s32 new_window_height, float new_window_scale)
 {
-	if (m_swap_chain->GetWidth() == new_window_width && m_swap_chain->GetHeight() == new_window_height)
+	if (m_swap_chain->GetWidth() == static_cast<u32>(new_window_width) && m_swap_chain->GetHeight() == static_cast<u32>(new_window_height))
 	{
 		// skip unnecessary resizes
 		m_window_info.surface_scale = new_window_scale;

pcsx2/GS/GSState.cpp

@@ -1772,8 +1772,6 @@ inline bool GSState::TestDrawChanged()
 
 void GSState::FlushPrim()
 {
-	const u32 new_prim = PRIM->U32[0];
-
 	if (m_index.tail > 0)
 	{
 		GL_REG("FlushPrim ctxt %d", PRIM->CTXT);