drm/plane: Fix create_in_format_blob() return value

In the Linux kernel, the following vulnerability has been resolved: drm/plane: Fix create_in_format_blob() return value create_in_format_blob() is either supposed to return a valid pointer or an error, but never NULL. The caller will dereference the blob when it is not an error, and thus will oops if NULL returned. Return proper error values in the failure cases.