doc: Fix typo in doucmentations

Correct typo (double words) in documentations.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/filesystems/nfs/pnfs.txt

@@ -12,7 +12,7 @@ struct pnfs_layout_hdr
 ----------------------
 The on-the-wire command LAYOUTGET corresponds to struct
 pnfs_layout_segment, usually referred to by the variable name lseg.
-Each nfs_inode may hold a pointer to a cache of of these layout
+Each nfs_inode may hold a pointer to a cache of these layout
 segments in nfsi->layout, of type struct pnfs_layout_hdr.
 
 We reference the header for the inode pointing to it, across each