spl: fit: Don't overwrite previous loadable if "load" is missing

spl: fit: Don't overwrite previous loadable if "load" is missing

spl_load_fit_image() will try to load an image at the address given
in the "load" property. Absent such property, it uses

	image_info->load_addr

Correct use of this is demonstrated in spl_fit_append_fdt(), which
resets the 'load_addr' before each spl_load_fit_image() call.

On the other hand loading "loadables" loop in spl_load_simple_fit()
completely ignores this. It re-uses the same structure, but doesn't
reset load_addr. If loadable [i] does not have a "load" property, its
load address defaults to load_addr, which still contains the address
of loadable [i - 1].

A simple solution is to treat NULL as an invalid load address. The
caller can set load_addr = 0 to request an abort if the "load"
property is absent.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>