tests: Fix grpform_wait_peer group removal in P2P Device case

Get the P2P group interface name so it will be used for group removal to
support configurations that use a dedicated P2P Device interface.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>

tests/hwsim/test_p2p_grpform.py

@@ -877,6 +877,8 @@ def test_grpform_wait_peer(dev):
     ev = dev[0].wait_global_event(["P2P-GROUP-STARTED"], timeout=15)
     if ev is None:
         raise Exception("Group formation timed out")
+    dev[0].group_form_result(ev)
+
     dev[0].request("SET extra_roc_dur 0")
     ev = dev[1].wait_global_event(["P2P-GROUP-STARTED"], timeout=15)
     if ev is None: