[U-Boot] u-boot-dm failures in "ut dm bootcount"

Simon,

In the latest u-boot-dm.git, sandbox fails as follows:

=> ut dm bootcount Test: dm_test_bootcount: bootcount.c /var/lib/jenkins/workspace/u-boot-denx_uboot_dm-master-build/src/u-boot/test/dm/bootcount.c:18, dm_test_bootcount(): 0 == uclass_get_device(UCLASS_BOOTCOUNT, 0, &dev): Expected 0, got -19 Test: dm_test_bootcount: bootcount.c (flat tree) /var/lib/jenkins/workspace/u-boot-denx_uboot_dm-master-build/src/u-boot/test/dm/bootcount.c:18, dm_test_bootcount(): 0 == uclass_get_device(UCLASS_BOOTCOUNT, 0, &dev): Expected 0, got -19 Failures: 2