dmaengine: bcm2835: Fix descriptors usage for 40-bits channels

The bcm2835_dma_create_cb_chain() function is in charge of building up
the descriptors chain for a given transfer.

It was initially supporting only the BCM2835-style DMA controller, and
was later expanded to support controllers with 40-bits channels that use
a different descriptor layout.

However, some part of the function only use the old style descriptor,
even when building a chain of new-style descriptors, resulting in weird
bugs.

Fixes: 9a52a991 ("bcm2835-dma: Add proper 40-bit DMA support")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>