[U-Boot] spl: atf: pass NULL for bl32_ep pc

[Philipp Tomsich]

> ATF use bl32_ep_info->pc to decide if thre is an available bl32,
> let's mark it as NULL first.
> 
> Signed-off-by: Kever Yang <kever.yang at rock-chips.com>
> ---
> 
>  common/spl/spl_atf.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 

Reviewed-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>