regmap: regmap_raw_read return error on !bus->read

Return -ENOTSUPP if map->bus->read is not implemented and we do not use
the cache. This code path would directly use bus->read would run into an
NULL pointer for the read function.
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/regmap.c

@@ -2184,6 +2184,11 @@ int regmap_raw_read(struct regmap *map, unsigned int reg, void *val,
 
 	if (regmap_volatile_range(map, reg, val_count) || map->cache_bypass ||
 	    map->cache_type == REGCACHE_NONE) {
+		if (!map->bus->read) {
+			ret = -ENOTSUPP;
+			goto out;
+		}
+
 		/* Physical block read if there's no cache involved */
 		ret = _regmap_raw_read(map, reg, val, val_len);