NFS: Fix a warning in nfs4_async_handle_error

We're not modifying the nfs_server when we call nfs_inc_server_stats and
friends, so allow the compiler to pass 'const' pointers too.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/iostat.h b/fs/nfs/iostat.h
index 2ec65e1..a369528 100644
--- a/fs/nfs/iostat.h
+++ b/fs/nfs/iostat.h
@@ -19,7 +19,7 @@
 	unsigned long		events[__NFSIOS_COUNTSMAX];
 } ____cacheline_aligned;
 
-static inline void nfs_inc_server_stats(struct nfs_server *server,
+static inline void nfs_inc_server_stats(const struct nfs_server *server,
 					enum nfs_stat_eventcounters stat)
 {
 	struct nfs_iostats *iostats;
@@ -31,13 +31,13 @@
 	put_cpu_no_resched();
 }
 
-static inline void nfs_inc_stats(struct inode *inode,
+static inline void nfs_inc_stats(const struct inode *inode,
 				 enum nfs_stat_eventcounters stat)
 {
 	nfs_inc_server_stats(NFS_SERVER(inode), stat);
 }
 
-static inline void nfs_add_server_stats(struct nfs_server *server,
+static inline void nfs_add_server_stats(const struct nfs_server *server,
 					enum nfs_stat_bytecounters stat,
 					unsigned long addend)
 {
@@ -50,7 +50,7 @@
 	put_cpu_no_resched();
 }
 
-static inline void nfs_add_stats(struct inode *inode,
+static inline void nfs_add_stats(const struct inode *inode,
 				 enum nfs_stat_bytecounters stat,
 				 unsigned long addend)
 {