[NFC] Fix buildbot fail by add riscv64-registered-target

Author: BeMg

llvm/test/MachineVerifier/RISCV/subreg-liveness.mir

@@ -1,5 +1,6 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
 # RUN: llc -mtriple=riscv64 -mattr=+v -run-pass=none %s -o - | FileCheck %s
+# REQUIRES: riscv64-registered-target
 
 # During the MachineVerifier, it assumes that used registers have been defined
 # In this test case, while $v12_v13_v14_v15_v16 covers $v14_v15,