kernel/user.c: Use list_for_each_entry instead of list_for_each

kernel/user.c: Convert list_for_each to list_for_each_entry in
uid_hash_find()

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>