USB: serial: Eliminate useless code

The variables priv and portdata are initialized twice to the same (side
effect-free) expressions.  Drop one initialization in each case.

A simplified version of the semantic match that finds this problem is:
(http://coccinelle.lip6.fr/

)

// <smpl>
@forall@
idexpression *x;
identifier f!=ERR_PTR;
@@

x = f(...)
... when != x
(
x = f(...,<+...x...+>,...)
|
* x = f(...)
)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>