staging: dgnc: remove variable rc

Found using coccinelle script:
@@
local idexpression ret;
expression e;
@@

-ret =
+return
     e;
-return ret;

Signed-off-by: Aastha Gupta <aastha.gupta4104@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>