tests: Return a failure code when any tests fail

At present 'make check' succeeds even if some tests fail. Adjust this so
that we can use things like 'git bisect run make check' to find a failure.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/run_tests.sh

@@ -900,3 +900,4 @@ fi
 echo "* Strange test result:	$tot_strange"
 echo "**********"
 
+[ "$tot_tests" -eq "$tot_pass" ] || exit 1