contrib: Show actual default build dir in linux_build_toolchain.sh

Need to use BUILD_DIR instead of WORKSPACE as the latter hasn't been
set at this point.

Signed-off-by: Keith Packard <[email protected]>

contrib/linux_build_toolchain.sh

@@ -21,7 +21,7 @@ function usage()
 	echo "     Default is ${SDK_DIR}"
 	echo ""
 	echo "  -o Build directory, for building artifacts and final output. Optional."
-	echo "     Default is ${WORKSPACE}"
+	echo "     Default is ${BUILD_DIR}"
 	echo ""
 	echo "  -h This help."
 	echo ""