spi: Fix typo in header

Spelling.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/include/spi.h b/include/spi.h
index ef8c1f6..2d34e4a 100644
--- a/include/spi.h
+++ b/include/spi.h
@@ -51,7 +51,7 @@
  * struct from a spi_slave, use dev_get_parent_platdata(dev) or
  * dev_get_parent_platdata(slave->dev).
  *
- * This data is immuatable. Each time the device is probed, @max_hz and @mode
+ * This data is immutable. Each time the device is probed, @max_hz and @mode
  * will be copied to struct spi_slave.
  *
  * @cs:		Chip select number (0..n-1)