[autotest] Rename provision.FW_VERSION_PREFIX to provision.FW_RW_VERSION_PREFIX

To make it clear that the build is for updating RW firmware.

BUG=chromium:270258
TEST=local run_suite
./run_suite.py -b veyron_jerry -i trybot-veyron_jerry-paladin/R45-7122.0.0-b11 \
--firmware_rw_build veyron_jerry-firmware/R41-6588.106.0 --test_source_build \
 veyron_jerry-firmware/R41-6588.106.0 -p suites -s dummy

Change-Id: I842f348bc1ba567c5622ac126e8ca35392506774
Reviewed-on: https://chromium-review.googlesource.com/281623
Trybot-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
diff --git a/frontend/afe/rpc_interface.py b/frontend/afe/rpc_interface.py
index 584e481..2af5783 100644
--- a/frontend/afe/rpc_interface.py
+++ b/frontend/afe/rpc_interface.py
@@ -811,7 +811,7 @@
         builds = {}
         builds[provision.CROS_VERSION_PREFIX] = image
         if firmware_rw_build:
-            builds[provision.FW_VERSION_PREFIX] = firmware_rw_build
+            builds[provision.FW_RW_VERSION_PREFIX] = firmware_rw_build
         if firmware_ro_build:
             builds[provision.FW_RO_VERSION_PREFIX] = firmware_ro_build
         return site_rpc_interface.create_suite_job(