media: mxl5xx/stv0910/stv6111/ddbridge: fix MODULE_LICENSE to 'GPL v2'

In commit 3db30defab4b ("use correct MODULE_LINCESE for GPL v2 only
according to notice in header") in the upstream repository for the
mentioned four drivers at https://github.com/DigitalDevices/dddvb.git


(plus a few more which aren't part of the mainline kernel tree), the
MODULE_LICENSE was fixed to "GPL v2" and are now in sync with the
GPL copyright boilerplate. Apply this change to the kernel tree
drivers as well.

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>