Staging: udlfb: fix printk format warning

Fix printk format warning: use %td for ptrdiff:

drivers/staging/udlfb/udlfb.h:209: warning: format '%d' expects type 'int', but argument 3 has type 'long int'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>