kernel: backport mtk_ppe busy-wait loop fix

kernel: backport mtk_ppe busy-wait loop fix

Fixes logic that leads to this error when booting mt7621 and other
devices that use the mediatek ethernet driver:
  [   23.144378] mtk_soc_eth 1e100000.ethernet: PPE table busy

Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=c5d66587b8900201e1530b7c18d41e87bd5812f4
Fixes: f07fe36f22fc ("kernel: update flow offload patches to upstream version")
Cc: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>