drm/vc4: Fix oops dereferencing DPI's connector since panel_bridge.

In the cleanup, I didn't notice that we needed to dereference the
connector for the bus_format.  Fix the regression by looking up the
first (and only) connector attached to us, and assume that its
bus_format is what we want.  Some day it would be good to have that
part of display_info attached to the bridge, instead.

v2: Fix stray whitespace change

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: 7b1298e0 ("drm/vc4: Switch DPI to using the panel-bridge helper.")
Link: https://patchwork.freedesktop.org/patch/msgid/20180309233256.1667-1-eric@anholt.net


Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>