[roll] Roll fuchsia [brcmfmac] Shutdown async loop during release.

There is a very small window during release where async work can access
resources that are being deallocated. This can cause crashes during
shutdown.

Fix this by explicitly shutting down the async loop at the very
beginning of the release cycle, before resources are deallocated. This
will ensure that any pending asynchronous work is completed and no
further work is started.

Original-Bug: 89929
Test: ffx driver restart /system/driver/brcmfmac.so
      fx test brcmfmac_sim_test brcmfmac_test
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/620802
Original-Revision: f15e7198e68b3d1819f8a2964ae5b1dcd9e1818f
GitOrigin-RevId: 6378b4f958599d5dbd6290a696cb57b686ca6835
Change-Id: I19be1977a99e7619f39353866179dffdfc16ead2
diff --git a/stem b/stem
index f1f8cc5..c1fcbbc 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="242730e7b3e1b8db59a2fa53c73d32a4efa7920b"/>
+             revision="f15e7198e68b3d1819f8a2964ae5b1dcd9e1818f"/>
   </projects>
   <hooks>
     <hook name="install-environment"