dm: Rename disk uclass to ahci

This started as 'ahci' and was renamed to 'disk' during code review. But it
seems that this is too generic. Now that we have a 'blk' uclass, we can use
that as the generic piece, and revert to ahci for this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index a43492f..b832ae1 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -7,7 +7,7 @@
 
 obj-$(CONFIG_BLK) += blk-uclass.o
 
-obj-$(CONFIG_DISK) += disk-uclass.o
+obj-$(CONFIG_AHCI) += ahci-uclass.o
 obj-$(CONFIG_SCSI_AHCI) += ahci.o
 obj-$(CONFIG_DWC_AHSATA) += dwc_ahsata.o
 obj-$(CONFIG_FSL_SATA) += fsl_sata.o