V4L/DVB (12481): Fix lowband tuning with tda8261

Attached is a patch which fixes tuning to low frequency channels with
stb0899+tda8261 cards like the KNC TV-Station DVB-S2.
The cause of the issue was a broken if construct, which should have been
an if/else if, so that the setting for the lowest matching frequency is
applied.

Without this patch for example tuning to "arte" on Astra 19.2, 10744MHz
SR22000 failed most times and when it failed the communication between
driver and tda8261 was completely broken.
This problem disappears with the attached patch.

Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>