pxamci: correct DMA flow control

The DMA flow control in pxamci_setup_data() is backwards; fix it.

Signed-off-by: Matt Reimer <mreimer@sdgsystems.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>