kernel: fix busy wait loop in mediatek PPE code

The intention is for the loop to timeout if the body does not succeed.
The current logic calls time_is_before_jiffies(timeout) which is false
until after the timeout, so the loop body never executes.

time_is_after_jiffies(timeout) will return true until timeout is less
than jiffies, which is the intended behavior here.

Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>