lantiq: fix warning if ltq_atm modules are missing

Fixes the following warning on first boot if the ltq_atm modules are
not included in the image:

  ls: /lib/modules/4.4.49/ltq_atm*: No such file or directory

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/lantiq/base-files/etc/board.d/02_network

@@ -164,9 +164,8 @@ WBMR300)
 
 esac
 
-if [ -n "$(ls /lib/modules/`uname -r`/ltq_atm*)" ]; then
+ls /lib/modules/$(uname -r)/ltq_atm* 1> /dev/null 2>&1 && \
 	ucidef_add_atm_bridge "$vpi" "$vci" "$encaps" "$payload"
-fi
 
 if lantiq_is_vdsl_system; then
 	interface_wan="ptm0"