ath9k: fix sparse complaint on aphy for debugfs

This fixes this sparse complaint:

  CHECK   drivers/net/wireless/ath/ath9k/debug.c
drivers/net/wireless/ath/ath9k/debug.c:548:34: warning: symbol 'aphy' shadows an earlier one
drivers/net/wireless/ath/ath9k/debug.c:491:26: originally declared here

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>