Staging: iio: return expression instead of return ret

Staging: iio: return expression instead of return ret

The following Coccinelle script was used to detect this:

@@
local idexpression ret;
expression e;
@@

-ret =
+return
       e;
-return ret;

Signed-off-by: Bo YU <tsu.yubo@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>