Fix ACPI vs proc_create_data() mismerge

acpi_device_dir() is NULL until all files are createst, so everyting is
created in straight in /proc/ and creation code warns.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>