apm821xx: wndr4700: restore sd-card media detection

This was not converted to the new, dt-based board name.

Fixes: e90dc8d272 ("apm821xx: convert to device-tree board detection")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/apm821xx/base-files/etc/rc.button/BTN_1

@@ -4,7 +4,7 @@
 
 BOARD=$(board_name)
 
-if [ $BOARD == "wndr4700" ]; then
+if [ $BOARD == "netgear,wndr4700" ]; then
 	case "$ACTION" in
 	released)
 		rmmod dwc2