ath5k: fix all endian issues reported by sparse

Changes-licensed-under: ISC
Signed-off-by: Pavel Roskin <proski@gnu.org>
Acked-by: Luis R. Rodriguez <mcgrof@winlab.rutgers.edu>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>