dmaengine: dw: Unify ret-val local variables naming

Currently there are two names utilized in the driver to keep the functions
call status: ret and err. For the sake of unification convert to using the
first version only.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Acked-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20240802075100.6475-7-fancer.lancer@gmail.com


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