dmaengine: sf-pdma: replace /** with /* for non-function comment

There are several comments starting from "/**" but not for function
comment purpose. It causes kernel-doc parsing wrong string. Replace
"/**" with "/*" to fix them.

Signed-off-by: Green Wan <green.wan@sifive.com>
Link: https://lore.kernel.org/r/20191118143554.16129-1-green.wan@sifive.com


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