Documentation/driver-api: dmaengine/provider: drop doubled word

Drop the doubled word "has".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Vinod Koul <vkoul@kernel.org>
Cc: dmaengine@vger.kernel.org
Link: https://lore.kernel.org/r/20200704034502.17199-2-rdunlap@infradead.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>