[nrf fromtree] samples: wifi: Fix missing CONFIG for the option

Missed adding CONFIG_ to the configuration option.

Signed-off-by: Chaitanya Tata <[email protected]>
(cherry picked from commit f840f66)
(cherry picked from commit baaca29)

Author: krish2718

samples/net/wifi/sample.yaml

@@ -64,7 +64,7 @@ tests:
       - nucleo_h723zg
   sample.net.wifi.nrf7002eb:
     extra_args:
-      - NRF70_UTIL=y
+      - CONFIG_NRF70_UTIL=y
       - CONFIG_NRF_WIFI_BUILD_ONLY_MODE=y
       - SHIELD=nrf7002eb
     platform_allow: