[S390] hypfs: Use "%u" instead of "%d" for unsigned ints in snprintf

For printing unsigned integers hypfs uses "%d" in snprintf(). This is wrong.
With this patch "%u" is used instead.

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>