Replace function call to user code with jump

stk500v2/main.cpp

@@ -594,9 +594,7 @@ int main()
 				chipEraseFlag = ChipEraseState::NONE;
 			}
 
-			typedef void (*jump_fn)() __attribute__((naked, noreturn));
-			constexpr jump_fn boot = 0x0000;
-			boot();
+			asm volatile("jmp 0x0000");
 		}
 	}