drivers/isdn: correct use of ! and &

drivers/isdn: correct use of ! and &

In commit e6bafba5b4765a5a252f1b8d31cbf6d2459da337 ("wmi: (!x & y)
strikes again"), a bug was fixed that involved converting !x & y to !(x
& y).  The code below shows the same pattern, and thus should perhaps be
fixed in the same way.

This is not tested and clearly changes the semantics, so it is only
something to consider.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@ expression E1,E2; @@
(
  !E1 & !E2
|
- !E1 & E2
+ !(E1 & E2)
)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>