MAINTAINERS: Add Green as SiFive PDMA driver maintainer

Update MAINTAINERS for SiFive PDMA driver.

Signed-off-by: Green Wan <green.wan@sifive.com>
Link: https://lore.kernel.org/r/20191107084955.7580-5-green.wan@sifive.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>