iwlwifi: add RATE_MCS_RATE_MSK

Throughout the code we use rate_n_flags & 0xff to extract the lower byte
of the rate_n_flags u32 that contains the information about the rate.
Add a #define and remove the use of the magic number.

Signed-off-by: Daniel Halperin <dhalperi@cs.washington.edu>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-agn-rs.c b/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
index 63b58ec..e394e49 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
@@ -115,13 +115,18 @@
 	/* FIXME:RS:          ^^    should be INV (legacy) */
 };
 
+static inline u8 rs_extract_rate(u32 rate_n_flags)
+{
+	return (u8)(rate_n_flags & RATE_MCS_RATE_MSK);
+}
+
 static int iwl_hwrate_to_plcp_idx(u32 rate_n_flags)
 {
 	int idx = 0;
 
 	/* HT rate format */
 	if (rate_n_flags & RATE_MCS_HT_MSK) {
-		idx = (rate_n_flags & 0xff);
+		idx = rs_extract_rate(rate_n_flags);
 
 		if (idx >= IWL_RATE_MIMO3_6M_PLCP)
 			idx = idx - IWL_RATE_MIMO3_6M_PLCP;
@@ -138,7 +143,8 @@
 	/* legacy rate format, search for match in table */
 	} else {
 		for (idx = 0; idx < ARRAY_SIZE(iwl_rates); idx++)
-			if (iwl_rates[idx].plcp == (rate_n_flags & 0xFF))
+			if (iwl_rates[idx].plcp ==
+					rs_extract_rate(rate_n_flags))
 				return idx;
 	}
 
@@ -239,11 +245,6 @@
 
 #define MCS_INDEX_PER_STREAM	(8)
 
-static inline u8 rs_extract_rate(u32 rate_n_flags)
-{
-	return (u8)(rate_n_flags & 0xFF);
-}
-
 static void rs_rate_scale_clear_window(struct iwl_rate_scale_data *window)
 {
 	window->data = 0;