dmaengine/dw_dmac: Update maintainer-ship

Nobody is currently maintaining dw_dmac. We are using dw_dmac for SPEAr13xx and
are currently maintaining it. After discussing with Vinod, sending this patch to
update maintainer-ship of dw_dmac.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Acked-by: Havard Skinnemoen <hskinnemoen@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>