PCI: label: remove #include of ACPI header to avoid warnings

I found that including acpi/apci_drivers.h is not necessary and
introduces these warnings:

In file included from drivers/pci/pci-label.c:32:
include/acpi/acpi_drivers.h:103: warning: ‘struct acpi_device’ declared inside parameter list
include/acpi/acpi_drivers.h:103: warning: its scope is only this definition or declaration, which is probably not what you want
include/acpi/acpi_drivers.h:107: warning: ‘struct acpi_pci_root’ declared inside parameter list

Signed-off-by: Shyam Iyer <shyam_iyer@dell.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>