regmap: Check readable regs in _regmap_read

Check if regs are readable.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 6a19515..b897c1a 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -1736,6 +1736,9 @@
 	if (map->cache_only)
 		return -EBUSY;
 
+	if (!regmap_readable(map, reg))
+		return -EIO;
+
 	ret = map->reg_read(context, reg, val);
 	if (ret == 0) {
 #ifdef LOG_DEVICE