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>

include/linux/sunrpc/svc.h

@@ -421,7 +421,8 @@ struct svc_version {
 struct svc_procedure {
 	/* process the request: */
 	__be32			(*pc_func)(struct svc_rqst *);
-	kxdrproc_t		pc_decode;	/* XDR decode args */
+	/* XDR decode args: */
+	int			(*pc_decode)(struct svc_rqst *, __be32 *data);
 	kxdrproc_t		pc_encode;	/* XDR encode result */
 	/* XDR free result: */
 	void			(*pc_release)(struct svc_rqst *);