ACPI / PCI: Include appropriate header file in pci_slot.c

Includes appropriate header file linux/pci-acpi.h in pci_slot.c
because functions acpi_pci_slot_enumerate(), acpi_pci_slot_remove()
and acpi_pci_slot_init() have their prototype declaratons in
linux/pci-acpi.h.

This eliminates the following warnings in pci_slot.c:
drivers/acpi/pci_slot.c:162:6: warning: no previous prototype for ‘acpi_pci_slot_enumerate’ [-Wmissing-prototypes]
drivers/acpi/pci_slot.c:174:6: warning: no previous prototype for ‘acpi_pci_slot_remove’ [-Wmissing-prototypes]
drivers/acpi/pci_slot.c:215:13: warning: no previous prototype for ‘acpi_pci_slot_init’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/pci_slot.c

···
 #include <linux/pci.h>
 #include <linux/acpi.h>
 #include <linux/dmi.h>
+#include <linux/pci-acpi.h>
 
 static bool debug;
 static int check_sta_before_sun;