pstore: Use dynamic spinlock initializer

The per-prz spinlock should be using the dynamic initializer so that
lockdep can correctly track it. Without this, under lockdep, we get a
warning at boot that the lock is in non-static memory.

Fixes: 10970449 ("pstore: Make spinlock per zone instead of global")
Fixes: 76d5692a

 ("pstore: Correctly initialize spinlock and flags")
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org