configs/warp7: Improve Wifi instructions

The "modprobe brcmfmac" command is not necessary because this driver
is automatically loaded.

Remove the "iwconfig" line as it is considered deprecated:

warning: `iwconfig' uses wireless extensions which will stop working for Wi-Fi 7 hardware; use nl80211

Remove the "-Dwext" parameter as it is not supported by the default kernel
configuration:

wlan0: Unsupported driver 'wext'

Tested Wifi by following the updated commands.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

board/warp7/readme.txt

@@ -107,11 +107,9 @@ To boot your newly created system:
 Using Wifi
 ==========
 
-# modprobe brcmfmac
-# iwconfig wlan0 essid ACCESSPOINTNAME
 # wpa_passphrase ACCESSPOINTNAME > /etc/wpa.conf
 (enter the wifi password and press enter)
-# wpa_supplicant -Dwext -iwlan0 -c /etc/wpa.conf &
+# wpa_supplicant -iwlan0 -c /etc/wpa.conf &
 # udhcpc -i wlan0
 # ping buildroot.org