drivers/net/wireless/{airo,ipw2100}: fix error handling bugs

airo:
* fix oops, if !CONFIG_PROC_FS (create_proc_entry always returns NULL)

* handle pci_register_driver() failure.  if it fails, we really do
  want to exit, rather than (as a comment indicates) return success
  because-we-are-a-library.

* #if 0 have_isa_dev variable, which is assigned a value but never used

ipw2100:
* handle sysfs_create_group() failure

* handle driver_create_file() failure

Signed-off-by: Jeff Garzik <jeff@garzik.org>