apm821xx: tidy up 10-fix-wifi-mac

This applies some cosmetic style fixes:
- remove useless echo
- remove double equal sign (specific to bash)
- add quotes for -n check

Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/apm821xx/base-files/etc/hotplug.d/ieee80211/10_fix_wifi_mac

@@ -1,10 +1,10 @@
 #!/bin/ash
 
-[ "$ACTION" == "add" ] || exit 0
+[ "$ACTION" = "add" ] || exit 0
 
 PHYNBR=${DEVPATH##*/phy}
 
-[ -n $PHYNBR ] || exit 0
+[ -n "$PHYNBR" ] || exit 0
 
 . /lib/functions.sh
 . /lib/functions/system.sh
@@ -14,7 +14,7 @@ board=$(board_name)
 case "$board" in
 netgear,wndap620|\
 netgear,wndap660)
-	echo $(macaddr_add $(mtd_get_mac_ascii u-boot-env baseMAC) $(($PHYNBR + 1)) ) > /sys${DEVPATH}/macaddress
+	macaddr_add $(mtd_get_mac_ascii u-boot-env baseMAC) $(($PHYNBR + 1)) > /sys${DEVPATH}/macaddress
 	;;
 *)
 	;;