USB: skeleton: Correct use of ! and &

Correct priority problem in the use of ! and &.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/

)

// <smpl>
@@ expression E; constant C; @@
- !E & C
+ !(E & C)
// </smpl>

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