ath9k: Add debugfs support for mac/baseband samples

This patch keep track of number of samples that includes
DMA debugs registers, PCU observe, CR, channel noise,
cycle conters, noisefloor history buffer and last N number
of tx and rx descriptor status. These samples are grouped
in table manner which dumping in debgufs.

Debugfs file location:
    <debugfs_mnt>/ieee80211/phy#/ath9k/samples

Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/init.c b/drivers/net/wireless/ath/ath9k/init.c
index d7761d1..dd71a5f 100644
--- a/drivers/net/wireless/ath/ath9k/init.c
+++ b/drivers/net/wireless/ath/ath9k/init.c
@@ -572,6 +572,7 @@
 	mutex_init(&sc->mutex);
 #ifdef CONFIG_ATH9K_DEBUGFS
 	spin_lock_init(&sc->nodes_lock);
+	spin_lock_init(&sc->debug.samp_lock);
 	INIT_LIST_HEAD(&sc->nodes);
 #endif
 	tasklet_init(&sc->intr_tq, ath9k_tasklet, (unsigned long)sc);