drm/panel: khadas: Fix error code in khadas_ts050_panel_add()

There is a copy and paste bug so it didn't return the correct error
code.

Fixes: b2152121 ("drm: panel: add Khadas TS050 panel driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/X9NEfmgGilaXJs2R@mwanda