ath5k: clean up some comments

This fixes a few misspellings, word repetitions, and some grammar
nits in ath5k comments.  No code changes.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath5k/dma.c b/drivers/net/wireless/ath/ath5k/dma.c
index 484f318..58bb6c5 100644
--- a/drivers/net/wireless/ath/ath5k/dma.c
+++ b/drivers/net/wireless/ath/ath5k/dma.c
@@ -377,11 +377,11 @@
  *
  * This function increases/decreases the tx trigger level for the tx fifo
  * buffer (aka FIFO threshold) that is used to indicate when PCU flushes
- * the buffer and transmits it's data. Lowering this results sending small
+ * the buffer and transmits its data. Lowering this results sending small
  * frames more quickly but can lead to tx underruns, raising it a lot can
  * result other problems (i think bmiss is related). Right now we start with
  * the lowest possible (64Bytes) and if we get tx underrun we increase it using
- * the increase flag. Returns -EIO if we have have reached maximum/minimum.
+ * the increase flag. Returns -EIO if we have reached maximum/minimum.
  *
  * XXX: Link this with tx DMA size ?
  * XXX: Use it to save interrupts ?