media: dvb-frontends/stv0910: cleanup and fix licensing boilerplates

The stv0910.h doesn't carry any header nor any licensing boilerplate at
all, so copy this from the main driver file stv0910.c.

[mchehab@kernel.org: kept only the part of this patch that copied
 the license from stv0910.c into stv0910.h]
Cc: Ralph Metzler <rjkm@metzlerbros.de>
Cc: Manfred Voelkel <mvoelkel@DigitalDevices.de>
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>