Currently a plain integer is being used to nullify the pointer
struct v3d_submit_ext *se. Use NULL instead. Cleans up sparse
warnings:
drivers/gpu/drm/v3d/v3d_gem.c:777:53: warning: Using plain integer as
NULL pointer
drivers/gpu/drm/v3d/v3d_gem.c:1010:45: warning: Using plain integer as
NULL pointer