V4L/DVB (13608): radio-sf16fmi: fix mute, add SF16-FMP to texts

Fix completely broken mute handling radio-sf16fmi.
The sound was muted immediately after tuning in KRadio.
Also fix typos and add SF16-FMP to the texts.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Acked-by: Petr Vandrovec <petr@vandrovec.name>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>