Changes

mslookup: don't ignore return value of write()

Fix GCC 13.2.0 refuses to build this with -Werror:

src/mslookup/osmo-mslookup-client.c: In function 'socket_client_respond_result':
src/osmo-hlr/src/mslookup/osmo-mslookup-client.c:432:9: error: ignoring return value of 'write' declared with attribute 'warn_unused_result' [-Werror=unused-result]
  432 |         write(c->ofd.fd, response, strlen(response));
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/mslookup/osmo-mslookup-client.c: In function 'socket_accept':
src/osmo-hlr/src/mslookup/osmo-mslookup-client.c:530:17: error: ignoring return value of 'write' declared with attribute 'warn_unused_result' [-Werror=unused-result]
  530 |                 write(c->ofd.fd, CSV_HEADERS, strlen(CSV_HEADERS));
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Change-Id: I4b2e5cabe5306a999197f7c98362d872a3739078