[roll] Roll fuchsia [kernel][riscv] save one instruction on syscall path

A freebie when using the ZBA extension, which is designed to help
compute indexes into things.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1163573
Original-Revision: 9d18abce50c83364a4a828f2b877df9140cc6384
GitOrigin-RevId: 684a0a6d06c22c077c424772f79a90ee16f681f0
Change-Id: Iec7b32a69418f1c04edbe740571157b1c8fdf00f

Author: Travis Geiselbrecht

stem

@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="03c41380707569b0a5f26ca6d85263904cc8060a"/>
+             revision="9d18abce50c83364a4a828f2b877df9140cc6384"/>
   </projects>
   <hooks>
     <hook name="install-environment"