openvswitch: fix odd_ptr_err.cocci warnings

net/openvswitch/vport-gre.c:188:5-11: inconsistent IS_ERR and PTR_ERR, PTR_ERR on line 189

 PTR_ERR should access the value just tested by IS_ERR

Semantic patch information:
 There can be false positives in the patch case, where it is the call
 IS_ERR that is wrong.

Generated by: scripts/coccinelle/tests/odd_ptr_err.cocci

CC: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>