[SPARC]: BUG_ON() Conversion in arch/sparc/kernel/ioport.c

this changes if() BUG(); constructs to BUG_ON() which is
cleaner and can better optimized away

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>