ath79: fix patching ath9k MAC address for MyNet WiFi Range Extender

The code line patching ath9k MAC address for this device contains
a wrong number of arguments including an unset "$mac", which
looks like a typo or copy/paste mistake.

This has been introduced already in the device support commit
745dee11ac ("ath79: add support for WD My Net Wi-Fi Range
Extender").

This patch just removes the "$mac" argument, leaving a formally
valid line. (No on-device test has been performed.)

Cc: Christian Lamparter <chunkeey@gmail.com>

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(cherry picked from commit 6b5303378315084bf080a6408c2ca5b2a911aa5d)

target/linux/ath79/base-files/etc/hotplug.d/firmware/10-ath9k-eeprom

@@ -188,7 +188,7 @@ case "$FIRMWARE" in
 		;;
 	wd,mynet-wifi-rangeextender)
 		ath9k_eeprom_extract "art" 4096 4096
-		ath9k_patch_fw_mac $(nvram get wl0_hwaddr) "$mac" 2
+		ath9k_patch_fw_mac $(nvram get wl0_hwaddr) 2
 		;;
 	*)
 		ath9k_eeprom_die "board $board is not supported yet"