From: Greg KH <greg@kroah.com>

Different architectures use different types for dev_t, so it is hard to
print dev_t variables out correctly.  Quite a lot of code is wrong now, and
will continue to be wrong when 64-bit dev_t is merged.

Greg's patch introduces a little wrapper function which can be used to
safely form a dev_t for printing.  I added the format_dev_t function as
well, which is needed for direct insertion in a printk statement.