Fixes warnings on some architectures:

../src/mm/chatty-mmsd.c: In function ‘chatty_mmsd_send_mms_create_attachments’:
../src/mm/chatty-mmsd.c:485:18: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 7 has type ‘gsize’ {aka ‘unsigned int’} [-Wformat=]
  485 |       g_warning ("Size of attachments that can't be resized %ld greater then maximum attachment size %d",
      |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  486 |                  other_attachments_size, self->max_attach_size);
      |                  ~~~~~~~~~~~~~~~~~~~~~~
      |                  |
      |                  gsize {aka unsigned int}
/usr/include/glib-2.0/glib/gmessages.h:323:63: note: in definition of macro ‘g_warning’
  323 |                                                    G_STRFUNC, __VA_ARGS__)
      |                                                               ^~~~~~~~~~~
../src/mm/chatty-mmsd.c:485:63: note: format string is defined here
  485 |       g_warning ("Size of attachments that can't be resized %ld greater then maximum attachment size %d",
      |                                                             ~~^
      |                                                               |
      |                                                               long int
      |                                                             %d