PCI: Include <linux/pci.h>, not <asm/pci.h>

We already include <asm/pci.h> from <linux/pci.h>, so just include
<linux/pci.h> directly.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: linuxppc-dev@lists.ozlabs.org
CC: linux-s390@vger.kernel.org