checkpatch.py: Fix false positive on if/when/for

checkpatch.py: Fix false positive on if/when/for

We need to use == instead of the is operator. If you're unlucky it may
fail because they're not exactly the same object, but hold the same
value.

Example false positive:

E(120): Inappropriate bracing around statement

+            if (0 != nl_attr_get_u8(vxlan[IFLA_VXLAN_LEARNING])

Fixes: 30c7ffd5ac46 ("utilities/checkpatch.py: Check for appropriate bracing")
Signed-off-by: Eric Garver <e@erig.me>
Signed-off-by: Russell Bryant <russell@ovn.org>