media: dvb-frontends/stv0910: change minsymrate to 100Ksyms/s

The demodulator supports symbol rates as low as 100Ksyms/s - the demod
setup in start() already handles such low symbol rates and reviewers
of stv0910 equipped cards even found and tested transponders with
SRs in that range. So, announce this in the fe_ops.

Cc: Ralph Metzler <rjkm@metzlerbros.de>
Cc: Richard Scobie <r.scobie@clear.net.nz>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>