net/nut: Fix typo is serial config option

Fixes: 5503dac806 "Add back serial support"
Reported-by: Znevna on irc
Signed-off-by: Karl Palsson <karlp@tweak.net.au>

net/nut/Makefile

@@ -500,7 +500,7 @@ CONFIGURE_ARGS += \
 	--$(if $(CONFIG_NUT_DRIVER_USB),with,without)-usb \
 	--without-avahi \
 	--$(if $(CONFIG_NUT_DRIVER_SNMP),with,without)-snmp \
-	--$(if $(CONFIG_NUT_DRIVER_SERAL),with,without)-serial \
+	--$(if $(CONFIG_NUT_DRIVER_SERIAL),with,without)-serial \
 	--without-neon \
 	--without-powerman \
 	--without-wrap \