Documentation: filesystems: caching/operations: drop doubled word

Drop the doubled word "be".

Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: [e-mail]
Cc: David Howells <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/filesystems/caching/operations.rst

···
 fscache_operation structs, though these are usually embedded into some other
 structure.
 
-This facility is available to and expected to be be used by the cache backends,
+This facility is available to and expected to be used by the cache backends,
 and FS-Cache will create operations and pass them off to the appropriate cache
 backend for completion.