PCI: cpqphp: Remove set but not used variable 'physical_slot'

Fixes gcc '-Wunused-but-set-variable' warning:

  drivers/pci/hotplug/cpqphp_core.c: In function 'init_SERR':
  drivers/pci/hotplug/cpqphp_core.c:124:5: warning: variable 'physical_slot' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>