[PATCH] debug_locks.h: add "struct task_struct;"

Removes many, many "declared inside parameter list" warnings on parisc.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>