Revert "[media] lmed04: add missing breaks"

According with Malcolm, the missing breaks are intentional.

So, let's revert commit d442b15fb4deb2b5d516e2dae1f569b1d5472399,
add some comments to document it and fix the two smatch warnings:

drivers/media/usb/dvb-usb-v2/lmedm04.c:828 lme_firmware_switch() warn: missing break? reassigning 'st->dvb_usb_lme2510_firmware'
drivers/media/usb/dvb-usb-v2/lmedm04.c:850 lme_firmware_switch() warn: missing break? reassigning 'st->dvb_usb_lme2510_firmware'

using a different strategy to avoid reassign values to
st->dvb_usb_lme2510_firmware.

Acked-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>