powerpc/gc/wii: hlwd-pic: convert irq_desc.lock to raw_spinlock

Fix the following build failures:

arch/powerpc/platforms/embedded6xx/hlwd-pic.c: In function 'hlwd_pic_irq_cascade':
arch/powerpc/platforms/embedded6xx/hlwd-pic.c:135: error: passing argument 1 of 'spin_lock' from incompatible pointer type
arch/powerpc/platforms/embedded6xx/hlwd-pic.c:137: error: passing argument 1 of 'spin_unlock' from incompatible pointer type
arch/powerpc/platforms/embedded6xx/hlwd-pic.c:145: error: passing argument 1 of 'spin_lock' from incompatible pointer type
arch/powerpc/platforms/embedded6xx/hlwd-pic.c:149: error: passing argument 1 of 'spin_unlock' from incompatible pointer type

These failures are caused by the changes introduced in commit
"genirq: Convert irq_desc.lock to raw_spinlock". The reason this driver
was not updated is that it wasn't merged yet.

Signed-off-by: Albert Herranz <albert_herranz@yahoo.es>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>