ath9k: Add wiphy name to log messages.

On systems with multiple NICs, it's nice to know which
one is producing warnings.  Here is an example of the
new ouput:

ath: wiphy0: Failed to stop TX DMA, queues=0x005!

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>