[mlir][target] Adjust the start and end position of the moduleToObject timer (#132693)

We hope that the timer can be cleared normally when the target-format is
`offload`, so as to avoid output like this:
```
===-------------------------------------------------------------------------===
Miscellaneous Ungrouped Timers
===-------------------------------------------------------------------------===

---Wall Time--- --- Name ---
----- Timer for perf llvm-ir -> isa and isa -> binary.
...
```

Co-authored-by: Guray Ozen <[email protected]>

Author: MikaOvO

mlir/lib/Target/LLVM/NVVM/Target.cpp

@@ -672,7 +672,6 @@ NVPTXSerializer::moduleToObject(llvm::Module &llvmModule) {
   llvm::Timer moduleToObjectTimer(
       "moduleToObjectTimer",
       "Timer for perf llvm-ir -> isa and isa -> binary.");
-  moduleToObjectTimer.startTimer();
   // Return LLVM IR if the compilation target is `offload`.
 #define DEBUG_TYPE "serialize-to-llvm"
   LLVM_DEBUG({
@@ -699,16 +698,17 @@ NVPTXSerializer::moduleToObject(llvm::Module &llvmModule) {
                                << triple << ", can't optimize with LLVM\n";
     return std::nullopt;
   }
+  moduleToObjectTimer.startTimer();
   std::optional<std::string> serializedISA =
       translateToISA(llvmModule, **targetMachine);
+  moduleToObjectTimer.stopTimer();
+  llvmToISATimeInMs = moduleToObjectTimer.getTotalTime().getWallTime() * 1000;
+  moduleToObjectTimer.clear();
   if (!serializedISA) {
     getOperation().emitError() << "Failed translating the module to ISA.";
     return std::nullopt;
   }
 
-  moduleToObjectTimer.stopTimer();
-  llvmToISATimeInMs = moduleToObjectTimer.getTotalTime().getWallTime() * 1000;
-  moduleToObjectTimer.clear();
   if (isaCallback)
     isaCallback(serializedISA.value());