ramips: do not "local" variables outside of a function

Older busybox versions allowed using the local keyword outside of
functions, whereas 1.25.0 (which was introduced in 06fa1c46fc) do not
allow this anymore (leading to the following error when executing the
script: "file: local: line nn: not in a function").

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

target/linux/ramips/base-files/etc/hotplug.d/firmware/10-rt2x00-eeprom

@@ -58,7 +58,7 @@ case "$FIRMWARE" in
 		rt2x00_eeprom_extract "factory" 32768 512
 		;;
 	tiny-ac)
-		local wifi_mac=$(mtd_get_mac_ascii u-boot-env INIC_MAC_ADDR)
+		wifi_mac=$(mtd_get_mac_ascii u-boot-env INIC_MAC_ADDR)
 		rt2x00_eeprom_extract "factory" 0 512
 		rt2x00_eeprom_set_macaddr $wifi_mac
 		;;