kernel/thread: Use owner_process when setting the page table in SetupMainThread()

The owning process of a thread is required to exist before the thread,
so we can enforce this API-wise by using a reference. We can also avoid
the reliance on the system instance by using that parameter to access
the page table that needs to be set.

src/core/hle/kernel/process.cpp

@@ -125,7 +125,7 @@ void Process::Run(VAddr entry_point, s32 main_thread_priority, u32 stack_size) {
     vm_manager.LogLayout();
     status = ProcessStatus::Running;
 
-    Kernel::SetupMainThread(kernel, entry_point, main_thread_priority, this);
+    Kernel::SetupMainThread(kernel, entry_point, main_thread_priority, *this);
 }
 
 void Process::LoadModule(SharedPtr<CodeSet> module_, VAddr base_addr) {

src/core/hle/kernel/thread.cpp

@@ -311,13 +311,13 @@ void Thread::BoostPriority(u32 priority) {
 }
 
 SharedPtr<Thread> SetupMainThread(KernelCore& kernel, VAddr entry_point, u32 priority,
-                                  SharedPtr<Process> owner_process) {
+                                  Process& owner_process) {
     // Setup page table so we can write to memory
-    SetCurrentPageTable(&Core::CurrentProcess()->vm_manager.page_table);
+    SetCurrentPageTable(&owner_process.vm_manager.page_table);
 
     // Initialize new "main" thread
     auto thread_res = Thread::Create(kernel, "main", entry_point, priority, 0, THREADPROCESSORID_0,
-                                     Memory::STACK_AREA_VADDR_END, std::move(owner_process));
+                                     Memory::STACK_AREA_VADDR_END, &owner_process);
 
     SharedPtr<Thread> thread = std::move(thread_res).Unwrap();
 

src/core/hle/kernel/thread.h

@@ -281,7 +281,7 @@ private:
  * @return A shared pointer to the main thread
  */
 SharedPtr<Thread> SetupMainThread(KernelCore& kernel, VAddr entry_point, u32 priority,
-                                  SharedPtr<Process> owner_process);
+                                  Process& owner_process);
 
 /**
  * Gets the current thread