video: fbdev: constify fb_fix_screeninfo and fb_var_screeninfo structures

These structures are only used to copy into other structures, so declare
them as const.

The semantic patch that makes this change in the fb_fix_screeninfo case is
as follows (http://coccinelle.lip6.fr/

).  The fb_var_screeninfo case is
analogous.

// <smpl>
@r disable optional_qualifier@
identifier i;
position p;
@@
static struct fb_fix_screeninfo i@p = { ... };

@ok@
identifier r.i;
expression e;
position p;
@@
e = i@p

@bad@
position p != {r.p,ok.p};
identifier r.i;
struct fb_fix_screeninfo e;
@@
e@i@p

@depends on !bad disable optional_qualifier@
identifier r.i;
@@
static
+const
 struct fb_fix_screeninfo i = { ... };
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>