regmap: drop cache if the bus transfer error

regmap_write
->_regmap_raw_write
-->regcache_write first and than use map->bus->write to wirte i2c or spi
But if the i2c or spi transfer failed, But the cache is updated, So if I use
regmap_read will get the cache data which is not the real register value.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/regmap.c

@@ -1474,6 +1474,8 @@ int _regmap_raw_write(struct regmap *map, unsigned int reg,
 		ret = map->bus->write(map->bus_context, buf, len);
 
 		kfree(buf);
+	} else if (ret != 0 && !map->cache_bypass && map->format.parse_val) {
+		regcache_drop_region(map, reg, reg + 1);
 	}
 
 	trace_regmap_hw_write_done(map, reg, val_len / map->format.val_bytes);