drm/radeon/kms: fix bugs in ddc and cd path router code

This is a follow on to:
2b5b1d7da9583484b3a9e7e375a90ca0e8ca07c2
(drm/radeon/kms: add support for clock/data path routers)

That patch completed mux support for ddc and cd line routing
between connectors.  This patch fixes an indexing typo that was
resulting in the atom bios router objects not always being walked,
ensures the validity entries for the reused router structure are
reset for every connector object walked, and corrects the masking
operations used to update the mux control bits.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=31339

Signed-off-by: Tyson Whitehead <twhitehead@gmail.com>
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>