iwlwifi: change rate number to a constant

This patch moves a number to an understandable define

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl4965-base.c b/drivers/net/wireless/iwlwifi/iwl4965-base.c
index d84a7f2..b78ca77 100644
--- a/drivers/net/wireless/iwlwifi/iwl4965-base.c
+++ b/drivers/net/wireless/iwlwifi/iwl4965-base.c
@@ -5450,8 +5450,9 @@
 			/*
 			 * If CCK != 1M then set short preamble rate flag.
 			 */
-			rates[i].flags |= (iwl4965_rates[i].plcp == 10) ?
-				0 : IEEE80211_RATE_SHORT_PREAMBLE;
+			rates[i].flags |=
+				(iwl4965_rates[i].plcp == IWL_RATE_1M_PLCP) ?
+					0 : IEEE80211_RATE_SHORT_PREAMBLE;
 		}
 	}
 }