pmqos: Do not send DBus method return message when PMQoS is not started

pmqos: Do not send DBus method return message when PMQoS is not started

When the PMQoS module receives PMQoS requests via DBus methods
invocation before its initialization, the module displays out the
message about that the module is not started yet and it returns a DBus
message to the sender. The following log message is displayed in the
systemd journal because of this DBus method return message sending:

pass[2132]: g_object_unref: assertion 'G_IS_OBJECT (object)' failed

Although this warning may not harm any parts of the system, it is fixed
by this patch as well.

Change-Id: I4f22e4b429c2dcbbd2f1834ec485dc06bfdf24a2
Signed-off-by: Wook Song <wook16.song@samsung.com>