ata: fix requirements for CONFIG_AHCI_PCI

Building with CONFIG_AHCI_PCI=y and CONFIG_SCSI_AHCI=n leads to

    drivers/ata/ahci-pci.o: in function `ahci_pci_probe':
    drivers/ata/ahci-pci.c:21: undefined reference to `ahci_probe_scsi_pci'

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/ata/Kconfig b/drivers/ata/Kconfig
index 3fe53d6..2ab502c 100644
--- a/drivers/ata/Kconfig
+++ b/drivers/ata/Kconfig
@@ -37,6 +37,7 @@
 	bool "Support for PCI-based AHCI controller"
 	depends on PCI
 	depends on DM_SCSI
+	depends on SCSI_AHCI
 	help
 	  Enables support for the PCI-based AHCI controller.