drm: panel-lvds: Potential Oops in probe error handling

drm: panel-lvds: Potential Oops in probe error handling

[ Upstream commit fb2ee9bf084bcaeff1e5be100decc0eacb4af2d5 ]

The "lvds->backlight" pointer could be NULL in situations where
of_parse_phandle() returns NULL.  This code is cleaner if we use the
managed devm_of_find_backlight() so the clean up is automatic.

Fixes: 7c9dff5bd643 ("drm: panels: Add LVDS panel driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190911104928.GA15930@mwanda
Signed-off-by: Sasha Levin <sashal@kernel.org>