core: Resolve misc cases of variable shadowing

Resolves shadowing warnings that aren't in a particularly large
subsection of core. Brings us closer to turning -Wshadow into an error.

All that remains now is for cases in the kernel (left untouched for now
since a big change by bunnei is pending), and a few left over in the
service code (will be tackled next).

src/core/core_timing.cpp

@@ -133,8 +133,8 @@ void CoreTiming::UnscheduleEvent(const std::shared_ptr<EventType>& event_type,
     }
 }
 
-void CoreTiming::AddTicks(u64 ticks) {
-    this->ticks += ticks;
+void CoreTiming::AddTicks(u64 ticks_to_add) {
+    ticks += ticks_to_add;
     downcount -= static_cast<s64>(ticks);
 }