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

[Stephen Warren]

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