ath9k: move duplicated debug message to 'ath9k_hw_nvram_read'

The fill_eeprom functions are printing the same
debug message in case the 'ath9k_hw_nvram_read'
function fails. Remove the duplicated code from
fill_eeprom functions and add the ath_dbg call
directly into 'ath9k_hw_nvram_read'.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>