dma-buf/sync_file: Fix docs syntax

Fixes the warning:

  include/uapi/linux/sync_file.h:77: warning: Function parameter or member 'num_fences' not described in 'sync_file_info'

Fixes: 2d75c88f ("staging/android: refactor SYNC IOCTLs")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20230724145000.125880-1-robdclark@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>