drivers/video/fbdev/omap/lcd_mipid.c: add const to lcd_panel structure

Make lcd_panel structure const as it is only copied to some object.
As the only usage of this structure is a copy operation, so it can be
made const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>