ath: use seq_file api for ath9k debugfs files

The debugfs files that are defined in debug.c which are read-only
and using a simple_open as .open file operation have been modified
to use the single_open seq_file API. This simplifies the read
functions defining the file contents.
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/wireless/ath/ath9k/debug.h

@@ -195,12 +195,11 @@ struct ath_tx_stats {
 #define TXSTATS sc->debug.stats.txstats
 #define PR(str, elem)							\
 	do {								\
-		len += scnprintf(buf + len, size - len,			\
-				 "%s%13u%11u%10u%10u\n", str,		\
-				 TXSTATS[PR_QNUM(IEEE80211_AC_BE)].elem,\
-				 TXSTATS[PR_QNUM(IEEE80211_AC_BK)].elem,\
-				 TXSTATS[PR_QNUM(IEEE80211_AC_VI)].elem,\
-				 TXSTATS[PR_QNUM(IEEE80211_AC_VO)].elem); \
+		seq_printf(file, "%s%13u%11u%10u%10u\n", str,		\
+			   TXSTATS[PR_QNUM(IEEE80211_AC_BE)].elem,\
+			   TXSTATS[PR_QNUM(IEEE80211_AC_BK)].elem,\
+			   TXSTATS[PR_QNUM(IEEE80211_AC_VI)].elem,\
+			   TXSTATS[PR_QNUM(IEEE80211_AC_VO)].elem); \
 	} while(0)
 
 struct ath_rx_rate_stats {