syntax: virPCIDeviceFree is also a NOP for NULL args

add it to the syntax-check list and fix the one offending caller.

cfg.mk

@@ -165,6 +165,7 @@ useless_free_options =				\
   --name=virNodeDeviceObjFree			\
   --name=virObjectUnref                         \
   --name=virObjectFreeCallback                  \
+  --name=virPCIDeviceFree                       \
   --name=virSecretDefFree			\
   --name=virStorageEncryptionFree		\
   --name=virStorageEncryptionSecretFree		\

src/util/virpci.c

@@ -1671,8 +1671,7 @@ virPCIDeviceListDel(virPCIDeviceListPtr list,
                     virPCIDevicePtr dev)
 {
     virPCIDevicePtr ret = virPCIDeviceListSteal(list, dev);
-    if (ret)
-        virPCIDeviceFree(ret);
+    virPCIDeviceFree(ret);
 }
 
 int