dm: fix typo falback

%s/falback/fallback/g

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/dm/uclass.h

@@ -72,11 +72,11 @@ struct udevice;
  * then this will be automatically allocated.
  * @per_child_auto_alloc_size: Each child device (of a parent in this
  * uclass) can hold parent data for the device/uclass. This value is only
- * used as a falback if this member is 0 in the driver.
+ * used as a fallback if this member is 0 in the driver.
  * @per_child_platdata_auto_alloc_size: A bus likes to store information about
  * its children. If non-zero this is the size of this data, to be allocated
  * in the child device's parent_platdata pointer. This value is only used as
- * a falback if this member is 0 in the driver.
+ * a fallback if this member is 0 in the driver.
  * @ops: Uclass operations, providing the consistent interface to devices
  * within the uclass.
  * @flags: Flags for this uclass (DM_UC_...)