omapfb: simplify the return expression of panel_dpi_connect

Simplify the return expression.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921082443.2591721-1-liushixin2@huawei.com