[PATCH] xtensa: struct semaphore.sleepers initialization

No one may sleep on us until we've been down()'d.  So on allocation,
initialize `sleepers' to 0, just like everyone else does.

Signed-off-by: Arthur Othieno <a.othieno@bluewin.ch>
Acked-by: Christian Zankel <chris@zankel.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>