FramebufferManager: Don't discard in ReinterpretPixelData

This was causing the depth buffer to be discarded as well, which
has an effect on mobiles (doesn't get loaded into tile memory).

If we find this is hindering performance (remember, the EFB is
only a 640x528 texture), it may be worth changing the interface to
support discarding only the colour buffer.

Source/Core/VideoCommon/FramebufferManager.cpp

@@ -277,9 +277,12 @@ bool FramebufferManager::ReinterpretPixelData(EFBReinterpretType convtype)
     return false;
 
   // Draw to the secondary framebuffer.
+  // We don't discard here because discarding the framebuffer also throws away the depth
+  // buffer, which we want to preserve. If we find this to be hindering performance in the
+  // future (e.g. on mobile/tilers), it may be worth discarding only the color buffer.
   m_efb_color_texture->FinishedRendering();
   g_renderer->BeginUtilityDrawing();
-  g_renderer->SetAndDiscardFramebuffer(m_efb_convert_framebuffer.get());
+  g_renderer->SetFramebuffer(m_efb_convert_framebuffer.get());
   g_renderer->SetViewportAndScissor(m_efb_framebuffer->GetRect());
   g_renderer->SetPipeline(m_format_conversion_pipelines[static_cast<u32>(convtype)].get());
   g_renderer->SetTexture(0, m_efb_color_texture.get());