Add the check for the return value of the ida_alloc in order to avoid
NULL pointer dereference.
Moreover, free allocated "ctx->id" if mdp_m2m_open fails later in order
to avoid memory leak.
Fixes: 61890ccaefaf ("media: platform: mtk-mdp3: add MediaTek MDP3 driver")
Signed-off-by: Jiasheng Jiang <jiasheng@xxxxxxxxxxx>