[media] sh_veu: keep power supply until the m2m context is released

In the sh_veu driver, only the interrupt handler 'sh_veu_bh'
can invoke the v4l2_m2m_job_finish() function.
So the hardware must be alive for handling interrupts
until returning from v4l2_m2m_ctx_release().

Signed-off-by: Katsuya Matsubara <matsu@igel.co.jp>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>