[RISCV][test] Correct +experimental-ztso attr to +ztso in test

This doesn't chane the test output, but means it's now testing what it's
supposed to.

Author: asb

llvm/test/CodeGen/RISCV/atomicrmw-cond-sub-clamp.ll

@@ -3,13 +3,13 @@
 ; RUN:   | FileCheck -check-prefix=RV32I %s
 ; RUN: llc -mtriple=riscv32 -mattr=+a -verify-machineinstrs < %s \
 ; RUN:   | FileCheck -check-prefix=RV32IA %s
-; RUN: llc -mtriple=riscv32 -mattr=+a,+experimental-ztso -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv32 -mattr=+a,+ztso -verify-machineinstrs < %s \
 ; RUN:   | FileCheck -check-prefix=RV32IA %s
 ; RUN: llc -mtriple=riscv64 -verify-machineinstrs < %s \
 ; RUN:   | FileCheck -check-prefix=RV64I %s
 ; RUN: llc -mtriple=riscv64 -mattr=+a -verify-machineinstrs < %s \
 ; RUN:   | FileCheck -check-prefix=RV64IA %s
-; RUN: llc -mtriple=riscv64 -mattr=+a,+experimental-ztso -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv64 -mattr=+a,+ztso -verify-machineinstrs < %s \
 ; RUN:   | FileCheck -check-prefix=RV64IA %s