drm/exynos: Fix exynos_dpi_remove() parameter

exynos_dpi_remove() should receive a exynos_drm_display but when
DRM_EXYNOS_DPI was disabled it was receiving a struct device resulting in
ia compiler warning.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>