drm/nv50: fix connector table parsing for some cards

The connector table index in the DCB entry for each output type is an
index into the connector table, and does *not* necessarily match up
with what was previously called "index" in the connector table entries
themselves.

Not real sure what that index is exactly, renamed to "index2" as we
still use it to prevent creating multiple TV connectors.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>