ath9k: make is2ghz consistent in ar9003_eeprom

Replace a "mode" variable indicating "is 5ghz" with an "is2ghz" variable
to make it consistent with other functions in the file.

Signed-off-by: Wenli Looi <wlooi@ucalgary.ca>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220326054754.27812-1-wlooi@ucalgary.ca