drm/exynos: Search for TE-gpio in DSI panel's node

TE-gpio, if defined, is placed in the panel's node, not the parent DSI
node. Change the devm_gpiod_get_optional() to gpiod_get_optional() and
pass proper device node to it. The code already has a proper cleanup
path, so it looks that the devm_* variant has been applied accidentally
during the conversion to gpiod API.

Fixes: ee6c8b5a ("drm/exynos: Replace legacy gpio interface for gpiod interface")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixed a typo.
Signed-off-by: Inki Dae <inki.dae@samsung.com>