hw/dma: Enhance error handling in loading description

hw/dma: Enhance error handling in loading description

Loading a description from memory may cause a bus-error. In this
case, the DMA should stop working, set the error flag, and return
the failure value.

When calling the loading a description function, it should be noticed
that the function may return a failure value. Breaking the loop in this
case is one of the possible ways to handle it.

Signed-off-by: Fea.Wang <fea.wang@sifive.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>