sunrpc/auth_gss: fix decoder callback prototypes

Declare the p_decode callbacks with the proper prototype instead of
casting to kxdrdproc_t and losing all type safety.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Trond Myklebust <trond.myklebust@primarydata.com>

net/sunrpc/auth_gss/gss_rpc_xdr.c

@@ -790,8 +790,9 @@ done:
 
 int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
 				struct xdr_stream *xdr,
-				struct gssx_res_accept_sec_context *res)
+				void *data)
 {
+	struct gssx_res_accept_sec_context *res = data;
 	u32 value_follows;
 	int err;
 	struct page *scratch;