net: sundance: Use tasklet_disable_in_atomic().

tasklet_disable() is used in the timer callback. This might be distangled,
but without access to the hardware that's a bit risky.

Replace it with tasklet_disable_in_atomic() so tasklet_disable() can be
changed to a sleep wait once all remaining atomic users are converted.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210309084242.209110861@linutronix.de