[media] stb0899: allow minimum symbol rate of 1000000

This makes minimum symbol rate driver capabilities on par with
windows driver, and allows tuning on linux to transponders that
have symbol rate below 5000000, too.
Patch was tested successfully on Eutelsat 16A transponders that
became reachable with it (1000000 < symbol rate < 5000000):
      * DVB/S  12507050 V  2532000 3/4
      * DVB/S2 12574000 V  4355000 3/4 8PSK
      * DVB/S  12593000 V  2500000 2/3
      * DVB/S  12596940 V  2848000 2/3
      * DVB/S  12600750 V  2500000 1/2
      * DVB/S  12675590 H  4248000 3/4

Signed-off-by: Zoran Turalija <zoran.turalija@gmail.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>