media: imx-jpeg: fix a bug of accessing array out of bounds

When error occurs in parsing jpeg, the slot isn't acquired yet, it may
be the default value MXC_MAX_SLOTS.
If the driver access the slot using the incorrect slot number, it will
access array out of bounds.
The result is the driver will change num_domains, which follows
slot_data in struct mxc_jpeg_dev.
Then the driver won't detach the pm domain at rmmod, which will lead to
kernel panic when trying to insmod again.

Signed-off-by: Ming Qian <ming.qian@nxp.com>
Reviewed-by: Mirela Rabulea <mirela.rabulea@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>