fs/nfs/pnfs_nfs.c: fix spelling typo and syntax error in comment

Fix spelling typo and syntax error in comment.

Suggested-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: k2ci <kernel-bot@kylinos.cn>
Signed-off-by: Jiangshan Yi <yijiangshan@kylinos.cn>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>