fix comment typos concerning "challenge"

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/sound/soc/imx/imx-ssi.c b/sound/soc/imx/imx-ssi.c
index 80b4fee..4fd13d0 100644
--- a/sound/soc/imx/imx-ssi.c
+++ b/sound/soc/imx/imx-ssi.c
@@ -23,7 +23,7 @@
  * between pcm data and GPIO status data changes. Our FIQ handler is not
  * able to handle this, hence this driver only works with 48000Hz sampling
  * rate.
- * Reading and writing AC97 registers is another challange. The core
+ * Reading and writing AC97 registers is another challenge. The core
  * provides us status bits when the read register is updated with *another*
  * value. When we read the same register two times (and the register still
  * contains the same value) these status bits are not set. We work