drm/vc4: hdmi: Use local vc4_hdmi directly

The function vc4_hdmi_connector_detect access its vc4_hdmi struct by
dereferencing the pointer in the structure vc4_dev. This will cause some
issues when we will have multiple HDMI controllers, so let's just use the
local variable for now instead of dereferencing that pointer all the time,
and we'll fix the local variable later.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/ef92c5582d3b2894128b2272a8ada7cbc20be3d9.1599120059.git-series.maxime@cerno.tech