adf: Zero out the mapping data

The adf_device_post_nocopy function eventually calls the
dma_buf_attach and dma_buf_map_attachment functions. If the
dma_buf_attach function succeeds but the dma_buf_map_attachment
function fails, both the adf_buffer_map function and the
adf_device_post_nocopy function will call the dma_buf_detach
function to tear down the same dma-buf attachment.

b/28447556
Change-Id: I8eb40486496fe2a2ae5dfa1be4b76a4af0d6b827
Signed-off-by: Dennis Cagle <d-cagle@codeaurora.org>