libosmo-mgcp: fix unsigned compared against 0 in mgcp_trunk_by_name()

e1_trunk_nr_from_epname() returns a signed integer:

  int e1_trunk_nr_from_epname(const char *epname);

mgcp_trunk_by_num() accepts a signed integer:

  struct mgcp_trunk *mgcp_trunk_by_num(const struct mgcp_config *cfg, int index);

Change-Id: Id333a6ddcefd37d82d19f9378ab87d1c02ffd7e3
Closes: CID#211333
1 file changed