media: vim2m: Fix abort issue

Currently, if start streaming -> stop streaming -> start streaming
sequence is executed, driver will end job prematurely, if ctx->translen
is higher than 1, because "aborting" flag is still set from previous
stop streaming command.

Fix that by clearing "aborting" flag in start streaming handler.

Fixes: 96d8eab5

 ("V4L/DVB: [v5,2/2] v4l: Add a mem-to-mem videobuf framework test device")
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>