selftests: add missing test result status in memory-hotplug test

it only prints FAIL status when test fails, but doesn't print PASS
status when test pass,this patch is to add PASS status in the test log.

Signed-off-by: Lei Yang <Lei.Yang@windriver.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>