fixing the build for the 91x ncp

Author: chirag-silabs

src/platform/silabs/efr32/BUILD.gn

@@ -70,7 +70,7 @@ static_library("efr32") {
     sources += [
       "../rs911x/BLEManagerImpl.cpp",
       "../rs911x/rsi_ble_config.h",
-      "../rs911x/wfx_sl_ble_init.c",
+      "../rs911x/wfx_sl_ble_init.cpp",
       "../rs911x/wfx_sl_ble_init.h",
     ]
   } else {