Documentation: fpga: dfl: change FPGA indirect article to an

Change use of 'a fpga' to 'an fpga'

Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20210608212350.3029742-4-trix@redhat.com


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