iwlagn: remove drvdata support from bus layer

Since the removal of the sysfs files, it is no
longer necessary to have upper layers control
the drvdata, so let the PCI driver have it for
itself completely.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>