FROMLIST: drm/mediatek: dp: drm_err => dev_err in HPD path to avoid NULL ptr

The function mtk_dp_wait_hpd_asserted() may be called before the
`mtk_dp->drm_dev` pointer is assigned in mtk_dp_bridge_attach().
Specifically it can be called via this callpath:
 - mtk_edp_wait_hpd_asserted
 - [panel probe]
 - dp_aux_ep_probe

Using "drm" level prints anywhere in this callpath causes a NULL
pointer dereference. Change the error message directly in
mtk_dp_wait_hpd_asserted() to dev_err() to avoid this. Also change the
error messages in mtk_dp_parse_capabilities(), which is called by
mtk_dp_wait_hpd_asserted().

While touching these prints, also add the error code to them to make
future debugging easier.

Fixes: 7eacba9a ("drm/mediatek: dp: Add .wait_hpd_asserted() for AUX bus")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
(am from https://patchwork.kernel.org/patch/13942094/)
(also found at https://lore.kernel.org/r/20250116094249.1.I29b0b621abb613ddc70ab4996426a3909e1aa75f@changeid)

UPSTREAM-TASK=b:391646448
BUG=b:390455848
TEST=Put printout in non-error case and see crash fixed

Change-Id: I29b0b621abb613ddc70ab4996426a3909e1aa75f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/6191527


Commit-Queue: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Sean Paul <sean@poorly.run>
Commit-Queue: Stephen Boyd <swboyd@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Auto-Submit: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Hubert Mazur <hmazur@google.com>