ath5k: name pci driver "ath5k" too

Call the ath5k pci driver struct "ath5k" too to be less
confusing in sysfs.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>