s390/pci: removes wrong PCI multifunction assignment

The assignment of the PCI device multifunction attribute
is set during the PCI device probe.
There is no need to set it here.

Let's do it right and remove this assignment.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>