glib.supp: make gobject_init() calloc also of the possible kind

It's currently marked only as reachable but Valgrind also finds it as possible:

==18842== 96 bytes in 1 blocks are possibly lost in loss record 2,029 of 2,284
==18842==    at 0x4837B65: calloc (vg_replace_malloc.c:762)
==18842==    by 0x49614AD: g_malloc0 (gmem.c:129)
==18842==    by 0x4A7013B: type_node_any_new_W (gtype.c:439)
==18842==    by 0x4A70609: type_node_fundamental_new_W (gtype.c:550)
==18842==    by 0x4A7855A: gobject_init (gtype.c:4406)
==18842==    by 0x4A78672: gobject_init_ctor (gtype.c:4493)