bbb: Adapt to changes in the latest upstream buildroot

Change-Id: I20617186322fab70f089f03833a7804a37bc037e
diff --git a/configs/czechlight_beaglebone_defconfig b/configs/czechlight_beaglebone_defconfig
index daa5146..9a86478 100644
--- a/configs/czechlight_beaglebone_defconfig
+++ b/configs/czechlight_beaglebone_defconfig
@@ -34,7 +34,7 @@
 # BR2_PACKAGE_VIM_RUNTIME is not set
 BR2_TARGET_ROOTFS_EXT2=y
 BR2_TARGET_ROOTFS_EXT2_4=y
-BR2_TARGET_ROOTFS_EXT2_BLOCKS=131072
+BR2_TARGET_ROOTFS_EXT2_SIZE="131072"
 BR2_TARGET_BAREBOX=y
 BR2_TARGET_BAREBOX_BOARD_DEFCONFIG="am335x"
 BR2_TARGET_BAREBOX_IMAGE_FILE="images/barebox-am33xx-beaglebone.img"