hle_ipc: Make WriteToOutgoingCommandBuffer()'s reference parameter const

This function doesn't modify anything within the reference Thread
instance.

src/core/hle/kernel/hle_ipc.cpp

@@ -201,7 +201,7 @@ ResultCode HLERequestContext::PopulateFromIncomingCommandBuffer(u32_le* src_cmdb
     return RESULT_SUCCESS;
 }
 
-ResultCode HLERequestContext::WriteToOutgoingCommandBuffer(Thread& thread) {
+ResultCode HLERequestContext::WriteToOutgoingCommandBuffer(const Thread& thread) {
     std::array<u32, IPC::COMMAND_BUFFER_LENGTH> dst_cmdbuf;
     Memory::ReadBlock(*thread.owner_process, thread.GetTLSAddress(), dst_cmdbuf.data(),
                       dst_cmdbuf.size() * sizeof(u32));

src/core/hle/kernel/hle_ipc.h

@@ -132,7 +132,7 @@ public:
     ResultCode PopulateFromIncomingCommandBuffer(u32_le* src_cmdbuf, Process& src_process,
                                                  HandleTable& src_table);
     /// Writes data from this context back to the requesting process/thread.
-    ResultCode WriteToOutgoingCommandBuffer(Thread& thread);
+    ResultCode WriteToOutgoingCommandBuffer(const Thread& thread);
 
     u32_le GetCommand() const {
         return command;