MAINTAINERS: 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 all references at MAINTAINERS file
to point to the https URL instead.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>