media: imx274: declare the correct number of controls

v4l2_ctrl_handler_init() expects a hint of how many controls this
handler is expected to refer to. Since this number here is always 4,
let's pass exactly 4.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>