[SPARC64]: Handle ISA devices with no 'regs' property.

And this points out that the return value from
isa_dev_get_resource() and the 'pregs' arg to
isa_dev_get_irq() are totally unused.

Based upon a patch from Richard Mortimer <richm@oldelvet.org.uk>

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