ath5k: merge ath5k_hw and ath5k_softc

Both ath5k_hw and ath5k_softc represent one instance of the hardware.
This duplication is historical and is not needed anymore.

Keep the name "ath5k_hw" for the merged structure and "ah" for the
variable pointing to it.  "ath5k_hw" is shorter than "ath5k_softc", more
descriptive and more widely used.

Put the combined structure to ath5k.h where the old ath5k_softc used to
be. Move some code from base.h to ath5k.h as needed.

Remove memory allocation for struct ath5k_hw and the corresponding error
handling.  Merge iobase and ah_iobase fields.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>