src: Use g_steal_pointer() more

src: Use g_steal_pointer() more

There are few places where the g_steal_pointer() is open coded.
Switch them to calling the g_steal_pointer() function instead.
Generated by the following spatch:

  @ rule1 @
  expression a, b;
  @@
    <...
  - b = a;
    ... when != b
  - a = NULL;
  + b = g_steal_pointer(&a);
    ...>

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>