kernel/shared_memory: Make Map() and Unmap() take the target process by reference rather than as a pointer

Both member functions assume the passed in target process will not be
null. Instead of making this assumption implicit, we can change the
functions to be references and enforce this at the type-system level.

src/core/hle/kernel/svc.cpp

@@ -796,7 +796,7 @@ static ResultCode MapSharedMemory(Handle shared_memory_handle, VAddr addr, u64 s
         return ERR_INVALID_MEMORY_RANGE;
     }
 
-    return shared_memory->Map(current_process, addr, permissions_type, MemoryPermission::DontCare);
+    return shared_memory->Map(*current_process, addr, permissions_type, MemoryPermission::DontCare);
 }
 
 static ResultCode UnmapSharedMemory(Handle shared_memory_handle, VAddr addr, u64 size) {
@@ -826,7 +826,7 @@ static ResultCode UnmapSharedMemory(Handle shared_memory_handle, VAddr addr, u64
         return ERR_INVALID_MEMORY_RANGE;
     }
 
-    return shared_memory->Unmap(current_process, addr);
+    return shared_memory->Unmap(*current_process, addr);
 }
 
 /// Query process memory