selftests: memory-hotplug: fix emit_tests regression

Commit 16c513b1
("selftests: memory-hotplug: silence test command echo")

introduced regression in emit_tests and results in the following
failure when selftests are installed and run. Fix it.

Running tests in memory-hotplug
========================================
./run_kselftest.sh: line 121: @./mem-on-off-test.sh: No such file or
directory
selftests: memory-hotplug [FAIL]

Fixes: 16c513b1

 (selftests: memory-hotplug: silence test command echo")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>