Removing the warning error to only the specified error

third_party/silabs/efr32_sdk.gni

@@ -133,7 +133,6 @@ template("efr32_sdk") {
   sdk_target_name = target_name
 
   config("${sdk_target_name}_config") {
-    cflags = []
     include_dirs = []
     libs = []
     if (defined(invoker.include_dirs)) {
@@ -484,7 +483,7 @@ template("efr32_sdk") {
 
         # This is kept due to the warning on the LWIP when on demand timer is added
         # TODO: remove this flag once the warning is fixed in SiSDK MATTER-3946
-        cflags += [ "-Wno-error" ]
+        cflags_c = [ "-Wno-implicit-function-declaration" ]
       }
     }
 
@@ -610,6 +609,7 @@ template("efr32_sdk") {
       ]
     }
 
+    cflags = []
     foreach(include_dir, _include_dirs) {
       cflags += [ "-isystem" + rebase_path(include_dir, root_build_dir) ]
     }