conf: Fix initialization value of 'multi' in PCI address

conf: Fix initialization value of 'multi' in PCI address

The 'multi' element in PCI address struct used as 'virTristateSwitch',
and its default value is 'VIR_TRISTATE_SWITCH_ABSENT'. Current PCI
process use 'false' to initialization 'multi', which is ambiguously
for assignment or comparison. This patch use '{0}' to initialize
the whole PCI address struct, which fix the 'multi' initialization
and makes code more simplify and explicitly.

Signed-off-by: Xian Han Yu <xhyubj@linux.vnet.ibm.com>