fbdev: fix modedb docs in fb_find_mode

Fix up the indenting that confused sphinx. To make sure we
don't have to make the examples unreadable with escaping just
put them in as block quotes, that seems the simplest solution.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[b.zolnierkie: ported over fbdev changes]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>