package/rpi-firmware: Bump version to kernel 3.12.25

This version bump, amongst other things, introduces
OMX_ImageFilterDeInterlaceFast, which is needed by
the upcoming xbmc/kodi version bump.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>