Changes

Fix uninitialized return value

Caught by gcc 14.2.1:

/osmo-remsim/src/client/user_simtrace2.c:153:16: warning: ‘rc’ may be used uninitialized [-Wmaybe-uninitialized]
  153 |         return rc;
      |                ^~
/home/pespin/dev/sysmocom/git/osmo-remsim/src/client/user_simtrace2.c:128:13: note: ‘rc’ was declared here
  128 |         int rc;
      |             ^~

Change-Id: If90892ff6e00be38cea6f6d3161bf2386351bb21