media: staging: rkisp1: stats: protect write to 'is_streaming' in start_streaming cb

The field stats->is_streaming is written in 'start_streaming' callback
without the stats->lock protection.
The isr might run together with the callback so 'spin_lock_irq'
should be used.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>