ath9k: cleanup try count for MRR in rate control

This has no functional change and just cleans up the code
to be more legible and removes a useless variable for
Multi Rate Retry.

For regular frames we use 2 retries for MRR segments [0-2].
For the last MRR segment [3] we use 4.

MRR[0] = 2
MRR[1] = 2
MRR[2] = 2
MRR[3] = 4

Cc: Derek Smithies <derek@indranet.co.nz>
Cc: Chittajit Mitra <Chittajit.Mitra@Atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/main.c b/drivers/net/wireless/ath/ath9k/main.c
index 961b0ce..19df788 100644
--- a/drivers/net/wireless/ath/ath9k/main.c
+++ b/drivers/net/wireless/ath/ath9k/main.c
@@ -1540,7 +1540,8 @@
 	hw->max_rates = 4;
 	hw->channel_change_time = 5000;
 	hw->max_listen_interval = 10;
-	hw->max_rate_tries = ATH_11N_TXMAXTRY;
+	/* Hardware supports 10 but we use 4 */
+	hw->max_rate_tries = 4;
 	hw->sta_data_size = sizeof(struct ath_node);
 	hw->vif_data_size = sizeof(struct ath_vif);