Fix run-jdwp-tests.sh when running against RI.

We were incorrectly trying to pass --toolchain dx instead of
--toolchain javac when running against the RI.

Test: ./art/tools/run-jdwp-tests.sh --mode=jvm
Change-Id: Ie370afd6cb60fbad8e4171b94dd8885f674fface
diff --git a/tools/run-jdwp-tests.sh b/tools/run-jdwp-tests.sh
index db8c540..f5fbcd8 100755
--- a/tools/run-jdwp-tests.sh
+++ b/tools/run-jdwp-tests.sh
@@ -284,8 +284,10 @@
 
 if [[ $using_jack == "true" ]]; then
   toolchain_args="--toolchain jack --language JN --jack-arg -g"
-else
+elif [[ $mode != "ri" ]]; then
   toolchain_args="--toolchain dx --language CUR"
+else
+  toolchain_args="--toolchain javac --language CUR"
 fi
 
 # Run the tests using vogar.