Blackfin arch: fix bug - kernel boot fails when Spinlock and rw-lock debugging enabled

Initialize the lock of bad_irq_desc properly.
The content of irq_desc array is replaced by bad_irq_desc in blackfin
arch irqchip init code. So, do it properly as common irq init code.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>