drm: fix module name in edid_firmware log message

The module is drm_kms_helper, not drm_kms_firmware.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204549


Reported-by: Göran Uddeborg <goeran@uddeborg.se>
Fixes: ac6c35a4 ("drm: add backwards compatibility support for drm_kms_helper.edid_firmware")
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190821094312.5514-1-jani.nikula@intel.com