[Silabs] [WiFi] Build fix for the wifi devices when using 91x bluetooth (#28809)

* adding the header file for the RS911x ble in ncp mode

* restyling the PR
diff --git a/src/platform/silabs/rs911x/wfx_sl_ble_init.c b/src/platform/silabs/rs911x/wfx_sl_ble_init.c
index b62777d..1344847 100644
--- a/src/platform/silabs/rs911x/wfx_sl_ble_init.c
+++ b/src/platform/silabs/rs911x/wfx_sl_ble_init.c
@@ -22,6 +22,7 @@
  */

 #include "wfx_sl_ble_init.h"

 #include "ble_config.h"

+#include "cmsis_os2.h"

 #include "silabs_utils.h"

 // Global Variables

 rsi_ble_t att_list;