ACPI: fix section mismatch in acpi_pci_root_add

Fix following warning:
WARNING: vmlinux.o(.text+0x550e85): Section mismatch in reference from the function acpi_pci_root_add() to the function .devinit.text:pci_acpi_scan_root()

acpi_pci_root_add uses a __devinit annotated function and
it looks like annotating it __devinit too is the correct fix.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Len Brown <len.brown@intel.com>