dvb: switch play to record when there's not enough devices for both

Change the current behavior when there's a scheduled record that
has started while the device is playing another DVB channel: before
this change, it was stopping the play. Now, it will switch the
player to the new channel, if it is not at the same transponder.

BUG: 393647

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>