fixup! add fixedStack

Author: michaelmaitland

llvm/test/CodeGen/RISCV/rda-stack.mir

@@ -152,6 +152,9 @@ body:             |
 ---
 name:            test4
 tracksRegLiveness: true
+fixedStack:
+  - { id: 0, type: default, offset: 0, size: 4, alignment: 16,
+      isImmutable: true, isAliased: false }
 stack:
   - { id: 0, name: '', type: default, offset: 0, size: 4, alignment: 4,
       stack-id: default, callee-saved-register: '', callee-saved-restored: true,