NFS: trace: show TIMEDOUT instead of 0x6e

__nfs_revalidate_inode may return ETIMEDOUT.

print symbol of ETIMEDOUT in nfs trace:

before:
cat-5191 [005] 119.331127: nfs_revalidate_inode_exit: error=-110 (0x6e)

after:
cat-1738 [004] 44.365509: nfs_revalidate_inode_exit: error=-110 (TIMEDOUT)

Signed-off-by: Chen Hanxiao <chenhx.fnst@fujitsu.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>