[NFC][LoongArch] Update test for #94590

Author: heiher

llvm/test/CodeGen/LoongArch/opt-pipeline.ll

@@ -119,6 +119,7 @@
 ; LAXX-NEXT:       Register Coalescer
 ; LAXX-NEXT:       Rename Disconnected Subregister Components
 ; LAXX-NEXT:       Machine Instruction Scheduler
+; LAXX-NEXT:       LoongArch Dead register definitions
 ; LAXX-NEXT:       Machine Block Frequency Analysis
 ; LAXX-NEXT:       Debug Variable Analysis
 ; LAXX-NEXT:       Live Stack Slot Analysis