Staging: pi433: Merge assignment with return value

Removes the unnecessary assignment of retval preceding
the return statement.

Detected using the following Coccinelle script:
@@
local idexpression ret;
expression e;
@@

-ret =
+return
     e;
-return ret;

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>