ath9k: use AR_SREV_9003_PCOEM to identify PCOEM chips

commit f49c90db ("ath9k: Add a macro to identify PCOEM chips")
defined AR_SREV_9003_PCOEM macro, its more clear to use the macro
instead of checking one by one. Also removed PCOEM chips checking
in the callback of ar9003_hw_do_pcoem_manual_peak_cal() which only
for PCOEM chips.

Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>