[SPARC64]: Kill ugly __bucket() macro.

All the users go through virt_irq_to_bucket() and essentially
want to go from a virt_irq to an INO, but we have a way
to do that already via virt_to_real_irq_table[].dev_ino.

This also allows us to kill both virt_to_real_irq() and
virt_irq_to_bucket().

Signed-off-by: David S. Miller <davem@davemloft.net>