fat (exportfs): fix some kernel-doc warnings

Fix the following W=1 kernel build warning(s):

  fs/fat/nfs.c:21: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
  fs/fat/nfs.c:139: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Link: https://lkml.kernel.org/r/20221111075648.4005-1-liubo03@inspur.com
Signed-off-by: Bo Liu <liubo03@inspur.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Bo Liu

fs/fat/nfs.c

@@ -17,7 +17,7 @@ struct fat_fid {
 #define FAT_FID_SIZE_WITHOUT_PARENT 3
 #define FAT_FID_SIZE_WITH_PARENT (sizeof(struct fat_fid)/sizeof(u32))
 
-/**
+/*
  * Look up a directory inode given its starting cluster.
  */
 static struct inode *fat_dget(struct super_block *sb, int i_logstart)
@@ -135,7 +135,7 @@ fat_encode_fh_nostale(struct inode *inode, __u32 *fh, int *lenp,
 	return type;
 }
 
-/**
+/*
  * Map a NFS file handle to a corresponding dentry.
  * The dentry may or may not be connected to the filesystem root.
  */