Staging: comedi: Compressed two lines of code into one.

The following patch compressed two lines of code into one using
coccinelle and removed an unused variable.
The semantic patch used is as follows:

@@
expression ret;
identifier f;
@@

-ret =
+return
     f(...);
-return ret;

Signed-off-by: Heena Sirwani <heenasirwani@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>