dma/pl330: Fix buffer depth

dma/pl330: Fix buffer depth

This is the product of the data-width and the depth arguments, I.e the
depth of the FIFO is in terms of data entries and not bytes (which is
what the original implementation was suggesting). Fix.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: c34de31031511538ccdb3164b48ee8a6a973ebd4.1393372019.git.peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>