sunrpc: properly type pc_decode callbacks

Drop the argp argument as it can trivially be derived from the rqstp
argument.  With that all functions now have the same prototype, and we
can remove the unsafe casting to kxdrproc_t.

Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 4611cb7..18024c1 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1276,9 +1276,12 @@
 
 	/* Call the function that processes the request. */
 	if (!versp->vs_dispatch) {
-		/* Decode arguments */
-		xdr = procp->pc_decode;
-		if (xdr && !xdr(rqstp, argv->iov_base, rqstp->rq_argp))
+		/*
+		 * Decode arguments
+		 * XXX: why do we ignore the return value?
+		 */
+		if (procp->pc_decode &&
+		    !procp->pc_decode(rqstp, argv->iov_base))
 			goto err_garbage;
 
 		*statp = procp->pc_func(rqstp);