docs: fix supported_devices (missing newline)

I made the mistake of never looking at the rendered version
fixes 95e5d382
backport like 8b2cc206 is optional

(cherry picked from commit 41b2f002)

docs/user/supported_devices.rst

@@ -257,6 +257,7 @@ lantiq-xrx200
   - FRITZ!Box 7412 [#eva_ramboot]_
 
 * TP-Link
+
   - TD-W8970 (v1) [#lan_as_wan]_
 
 lantiq-xway