selftests/ftrace: Allow ":" in description

Allow ":" in the description line. Currently if there is ":"
in the test description line, the description is cut at that
point, but that was unintended.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>