w1: don't allow arbitrary users to remove w1 devices

The search/pullup/add/remove device attributes were 0666 which would allow
arbitrary users to affect the 1 wire bus.  Change to 0664 to prevent that.

I found this patch in the Android tree, apparently this has never been
sent upstream so doing it now.

Signed-off-by: Brian Swetland <swetland@google.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>