net: fix napi_disable() logic error

Dan reported a new warning after my recent patch:

New smatch warnings:
net/core/dev.c:6409 napi_disable() error: uninitialized symbol 'new'.

Indeed, we must first wait for STATE_SCHED and STATE_NPSVC to be cleared,
to make sure @new variable has been initialized properly.

Fixes: 4ffa1d1c ("net: adopt try_cmpxchg() in napi_{enable|disable}()")
Reported-by: Nkernel test robot <lkp@intel.com>
Reported-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -6399,9 +6399,9 @@ void napi_disable(struct napi_struct *n)
 
 	val = READ_ONCE(n->state);
 	do {
-		if (val & (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC)) {
+		while (val & (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC)) {
 			usleep_range(20, 200);
-			continue;
+			val = READ_ONCE(n->state);
 		}
 
 		new = val | NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC;