Documentation: fpga: eliminate duplicated word

Drop the doubled word "this".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Wu Hao <hao.wu@intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Wu Hao <hao.wu@intel.com>
Cc: linux-fpga@vger.kernel.org
Link: https://lore.kernel.org/r/20200707180414.10467-6-rdunlap@infradead.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>