nvdisp_disp0: Fix broken assert.

src/core/hle/service/nvdrv/devices/nvdisp_disp0.cpp

@@ -14,7 +14,7 @@ namespace NVDRV {
 namespace Devices {
 
 u32 nvdisp_disp0::ioctl(u32 command, const std::vector<u8>& input, std::vector<u8>& output) {
-    ASSERT(false, "Unimplemented");
+    UNIMPLEMENTED();
     return 0;
 }