[media] siano: Fix bandwidth report

It was expected that the bandwidth would be following the defines
at smscoreapi.h. However, this doesn't work. Instead, this field
brings just the bandwidth in MHz. Convert it to Hertz.
It should be noticed that, on ISDB, using the _EX request, the
field TuneBW seems to show the value that matches the bandwidth
code.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>