fix check prefix

Author: tgymnich

llvm/test/CodeGen/AArch64/popcount.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -O0 -mtriple=aarch64-unknown-unknown | FileCheck %s
+; RUN: llc < %s -O0 -mtriple=aarch64-unknown-unknown | FileCheck %s --check-prefix=CHECKO0
 ; RUN: llc < %s -mtriple=aarch64-unknown-unknown -mattr=+neon | FileCheck %s --check-prefixes=CHECK,NEON
 ; RUN: llc < %s -mtriple=aarch64-unknown-unknown -mattr=+neon,+dotprod | FileCheck %s --check-prefixes=CHECK,DOT
 ; RUN: llc < %s -mtriple=aarch64-unknown-unknown -mattr=+sve | FileCheck %s --check-prefixes=CHECK,SVE