dma/ste_dma40: explicitly include regulator consumer header

The patch "ARM: amba: Remove AMBA level regulator support" breaks
the DMA40 driver since the <linux/amba/bus.h> header implicitly
included the regulator consumer header. So include it explicitly
and fix the build error.

Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>