regmap: debugfs: fix possbile NULL pointer dereference

If 'map->dev' is NULL and there will lead dev_name() to be NULL pointer
dereference. So before dev_name(), we need to have check of the map->dev
pionter.

We also should make sure that the 'name' pointer shouldn't be NULL for
debugfs_create_dir(). So here using one default "dummy" debugfs name when
the 'name' pointer and 'map->dev' are both NULL.
Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org

(cherry picked from commit 2c98e0c1)
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

drivers/base/regmap/regmap-debugfs.c

@@ -382,6 +382,9 @@ void regmap_debugfs_init(struct regmap *map, const char *name)
 	if (map->dev)
 		devname = dev_name(map->dev);
 
+	if (map->dev)
+		devname = dev_name(map->dev);
+
 	if (name) {
 		map->debugfs_name = kasprintf(GFP_KERNEL, "%s-%s",
 					      devname, name);