printk_ratelimited(): fix uninitialized spinlock

ratelimit_state initialization of printk_ratelimited() seems broken.  This
fixes it by using DEFINE_RATELIMIT_STATE() to initialize spinlock
properly.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>