Documentation/driver-api: firmware/built-in-fw: drop doubled word

Drop the doubled word "for".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20200704034502.17199-3-rdunlap@infradead.org


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