parisc: BUG_ON() cleanup

- convert a few "if (xx) BUG();" to BUG_ON(xx)
- remove a few printk()s, as we get a backtrace with BUG_ON() anyway

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>