n_gsm: fix wait_event in gsmtty_modem_update when modem reset happened

n_gsm: fix wait_event in gsmtty_modem_update when modem reset happened

BZ: 14542

Scenario:
When gsmtty_modem_update send CMD_MSC to modem, it would stay in wait_event(ctrl->done) for control response.
If modem reset at this time, mux would never receive response from modem.
Then API open would stay in wait_event for ever, even if gsm_dlci_close.

The patch add "gsm->dead" condition in the wait_event of both gsm_control_send() and gsm_control_wait().
If gsm->dead, both gsm_control_send and gsm_control_wait should wake up from wait_event.

Change-Id: I1ad39a85686d1f1f1b75971c99f9450fa093b7db
Signed-off-by: samix.lebsir <samix.lebsir@intel.com>
Reviewed-on: http://android.intel.com:8080/29981
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>