uboot-phytec

efi_memory: avoid NULL dereference in efi_free_pool

If efi_free_pool is called with argument NULL an illegal memory
access occurs.

So let's check the parameter on entry.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>