ath5k: Check if pci pdev struct is initialized in common functions.

To be able to support other busses than PCI check if pci device
structure is initialized.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Wojciech Dubowik <Wojciech.Dubowik@neratec.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>