Convert the uses of fallthrough comments to fallthrough macro. Please see
commit 
294f69e662d1 ("compiler_attributes.h: Add 'fallthrough' pseudo
keyword for switch/case use") for detail.
Signed-off-by: Hongxiang Lou <louhongxiang@huawei.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
 
                default:
                        if (rpcauth_get_gssinfo(flavor, &info) != 0)
                                continue;
-                       /* Fallthrough */
+                       fallthrough;
                }
                dfprintk(MOUNT, "NFS: attempting to use auth flavor %u\n", flavor);
                ctx->selected_flavor = flavor;