replace functions which are only available in glib-2.24

replace functions which are only available in glib-2.24

Currently the minimal supported version of glib is 2.22.
Since testing is done with a glib that claims to be 2.22, but in fact
has APIs from newer version of glib, this bug was not caught during
submit of the patch referenced below.

Replace g_realloc_n, which is available only since 2.24, with g_renew.

Fixes commit 418026ca43 ("util: Introduce vfio helpers")

Signed-off-by: Olaf Hering <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Signed-off-by: Michael Tokarev <[email protected]>
CC: [email protected]