uboot-imx

bootm: allow correct bounds-check of destination

While nothing presently examines the destination size, it should at
least be correct so that future users of sys_mapmem() will not be
surprised. Without this, it might be possible to overflow memory.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>