fix minor infoleak in get_user_ex()

fix minor infoleak in get_user_ex()

get_user_ex(x, ptr) should zero x on failure.  It's not a lot of a leak
(at most we are leaking uninitialized 64bit value off the kernel stack,
and in a fairly constrained situation, at that), but the fix is trivial,
so...

Cc: [email protected]
Signed-off-by: Al Viro <[email protected]>
[ This sat in different branch from the uaccess fixes since mid-August ]
Signed-off-by: Linus Torvalds <[email protected]>