As the possible failure of the allocation, kmemdup() may return NULL
pointer.
Therefore, it should be better to check the return value of kmemdup()
and return error if fails.

Fixes: dc80d703 ("drm/imx-ldb: Add support to drm-bridge")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20220105074729.2363657-1-jiasheng@iscas.ac.cn