dm: regmap: Fix mask in regmap_update_bits()

This function assumes that the 'val' parameter has no masked bits set.
This is not defined by the function prototype though. Fix the function to
mask the value and update the documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
diff --git a/include/regmap.h b/include/regmap.h
index 0854200..9ada1af 100644
--- a/include/regmap.h
+++ b/include/regmap.h
@@ -295,7 +295,8 @@
  * @map:	The map returned by regmap_init_mem*()
  * @offset:	Offset of the memory
  * @mask:	Mask to apply to the read value
- * @val:	Value to apply to the value to write
+ * @val:	Value to OR with the read value after masking. Note that any
+ *	bits set in @val which are not set in @mask are ignored
  * Return: 0 if OK, -ve on error
  */
 int regmap_update_bits(struct regmap *map, uint offset, uint mask, uint val);