staging: greybus: loopback_test: fix comment style issues

According to checkpatch warning, block comments should align the * on
each line. Also, preferred style for multi-line comments is starting the
comment text after the second *.

Signed-off-by: Aleksey Rybalkin <aleksey@rybalkin.org>
Acked-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>