drm/bridge: imx8qxp-ldb: Remove dummy Runtime PM callback

drm/bridge: imx8qxp-ldb: Remove dummy Runtime PM callback

Since commit 63d00be69348fda4 ("PM: runtime: Allow unassigned
->runtime_suspend|resume callbacks"), unassigned
.runtime_{suspend,resume}() callbacks are treated the same as dummy
callbacks that just return zero.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Link: https://lore.kernel.org/r/c7436cda28409f0080dca6cd2ca13f142d6dc489.1756999913.git.geert+renesas@glider.be