MAINTAINERS: Step down from a co-maintaner of DW DMAC driver

As discussed at ELCE 2017 there is little to anticipate from me in the
future with regard to the driver, and since I have many things to keep
an eye on, I would like to step down to simple designated reviewer.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

MAINTAINERS

@@ -12885,7 +12885,7 @@ F:	Documentation/devicetree/bindings/arc/axs10*
 
 SYNOPSYS DESIGNWARE DMAC DRIVER
 M:	Viresh Kumar <vireshk@kernel.org>
-M:	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
+R:	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
 S:	Maintained
 F:	include/linux/dma/dw.h
 F:	include/linux/platform_data/dma-dw.h