media: atmel-isi: Fix crash due to missing subdev in state

As a result of converting to the stream-aware state functions, commit
bc0e8d91 ("media: v4l: subdev: Switch to stream-aware state
functions") caused the sd pointer of the state passed to the
v4l2_subdev_state_get_crop() function to be dereferenced. It however
missed that the atmel-isi driver creates the v4l2_subdev_state instance
on the stack (which it shouldn't do, but that's a separate problem),
without initializing the sd field. This results in a null pointer
dereference.

Fix it by initializing the sd field.

Fixes: bc0e8d91 ("media: v4l: subdev: Switch to stream-aware state functions")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>