WHENCE: use https://linuxtv.org for LinuxTV URLs

WHENCE: use https://linuxtv.org for LinuxTV URLs

While https was always supported on linuxtv.org, only in
Dec 3 2015 the website is using valid certificates.

As we're planning to drop pure http support on some
future, change the http://linuxtv.org references at firmware/WHENCE
file to point to https://linuxtv.org instead.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
[bwh: Adjust filename and context for the linux-firmware repository]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>