MAINTAINERS: add "C:" for URI for chat where developers hang out

MAINTAINERS: add "C:" for URI for chat where developers hang out

Make it easier to find the developer chat for the subsystem or driver.

Link: http://lkml.kernel.org/r/1476966135-26943-3-git-send-email-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>