media: i2c: imx219: Move variables to inner scope

The exposure_max, exposure_def and hblank variables are only used in an
inner scope in the imx219_set_pad_format() function. Move them to that
scope to keep them closer to their usage and improve readability.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>