bna: fix sparse warnings/errors

This fixes a several sparse warnings.
  * the __iomem tag was being used incorrectly (needs to be a prefix)
  * several variables should have been static since local to one file
  * the firmware was not being forwared declared
    and was const one place and not the other

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>