[media] solo6x10: Reduce OSD writes to the minimum necessary

Instead of unconditionally writing SOLO_EOSD_EXT_SIZE() bytes to the OSD
area (which is 64 or 128 kB depending on the PCI board) we only
write the actual amount of data needed which is 16 * OSD_TEXT_MAX (= 16 * 44).

Signed-off-by: Ismael Luceno <ismael.luceno@corp.bluecherry.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>