broadband-modem: initialize 'tac' in registration_status_check_ready()

mm-broadband-modem.c:4395:13: error: variable 'tac' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
        if (act == MM_MODEM_ACCESS_TECHNOLOGY_LTE) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm-broadband-modem.c:4407:75: note: uninitialized use occurs here
    mm_iface_modem_3gpp_update_location (MM_IFACE_MODEM_3GPP (self), lac, tac, cid);
                                                                          ^~~
mm-broadband-modem.c:4395:9: note: remove the 'if' if its condition is always true
        if (act == MM_MODEM_ACCESS_TECHNOLOGY_LTE) {
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm-broadband-modem.c:4380:9: error: variable 'tac' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
    if (cgreg) {
        ^~~~~
mm-broadband-modem.c:4407:75: note: uninitialized use occurs here
    mm_iface_modem_3gpp_update_location (MM_IFACE_MODEM_3GPP (self), lac, tac, cid);
                                                                          ^~~
mm-broadband-modem.c:4380:5: note: remove the 'if' if its condition is always false
    if (cgreg) {
    ^~~~~~~~~~~~
mm-broadband-modem.c:4280:15: note: initialize the variable 'tac' to silence this warning
    gulong tac;
              ^
               = 0
1 file changed