dma-debug: fix to not have dependency on get_dma_ops() interface

dma-debug depends on get_dma_ops() interface. Several architectures
do not define dma_ops and get_dma_ops(). When dma debug interfaces are
used on an architecture (e.g: c6x) that doesn't define get_dmap_ops(),
compilation fails. Changing dma-debug to call dma_mapping_error() instead
of defining its own that calls get_dma_ops(), such that the internal use of
dma_mapping_error() doesn't interfere with the debug_dma_mapping_error()
interface's mapping error checks. Moving dma_mapping_error() checks in
check_unmap() under the dma debug entry not found is sufficient to fix the
problem.

Reference: https://lkml.org/lkml/2012/10/26/367



Signed-off-by: Shuah Khan <shuah.khan@hp.com>
Reported-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>