Without this files in /dev/ appear as regular files. copy_file()
stumbles upon this as it tries a truncate() on that files which
then fails. Create the files as character devices so that copy_file()
works as expected.

Fixes: 9137c41915 ("fs: devfs: Switch to dentry cache implementation")

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Giorgio Dal Molin <giorgio.nicole@arcor.de>