drm/i915/wopcm: convert to drm device based logging

Prefer drm_dbg() over DRM_DEV_DEBUG_DRIVER() and drm_err() over
dev_err().

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/017d9bdc171481da13ba9492492625fc6878844d.1584714939.git.jani.nikula@intel.com