usb: misc: sisusbvga: compress return logic into one line

Simplify return logic to avoid unnecessary variable declaration
and assignment.

These issues were detected using Coccinelle and the following
semantic patch:

@@
local idexpression ret;
expression e;
@@

-ret =
+return
     e;
-return ret;

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>