disk: convert CONFIG_ISO_PARTITION to Kconfig

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay73@gmail.com>
diff --git a/disk/Makefile b/disk/Makefile
index 8b36b17..95d286b 100644
--- a/disk/Makefile
+++ b/disk/Makefile
@@ -10,6 +10,6 @@
 obj-$(CONFIG_PARTITIONS) 	+= part.o
 obj-$(CONFIG_$(SPL_)MAC_PARTITION)   += part_mac.o
 obj-$(CONFIG_$(SPL_)DOS_PARTITION)   += part_dos.o
-obj-$(CONFIG_ISO_PARTITION)   += part_iso.o
+obj-$(CONFIG_$(SPL_)ISO_PARTITION)   += part_iso.o
 obj-$(CONFIG_AMIGA_PARTITION) += part_amiga.o
 obj-$(CONFIG_EFI_PARTITION)   += part_efi.o