media: usb: add SPDX identifiers to some code I wrote

As we're now using SPDX identifiers, on several
media drivers I wrote, add the proper SPDX, identifying
the license I meant.

As we're now using the short license, it doesn't make sense to
keep the original license text.

Also, fix MODULE_LICENSE to properly identify GPL v2.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>