fdt: fix fdtdec_get_addr_size not to require any size cells

fdt: fix fdtdec_get_addr_size not to require any size cells

fdtdec_get_addr_size() may be used in two cases:
a) With sizep supplied, in which case both an address and a size are
parsed from DT. In this case, the DT property must be large enough to
contain both values.
b) With sizep NULL, in which case only an address is parsed from DT.
In this case, the DT property only need be large enough to contain this
address value. Commit 02464e386bb5 "fdt: add new fdt address parsing
functions" broke this relaxed checking, and required the DT property to
contain both an address and a size value in all cases.

Fix fdtdec_get_addr_size() to vary ns based on whether the size value
is being parsed from the DT or not. This is safe since the function only
parses the first entry in the property, so the overall value of (na + ns)
need not be accurate, since it is never used to step through the property
data to find other entries. Besides, this fixed behaviour essentially
matches the original behaviour before the patch this patch fixes. (The
original code validated that the property was exactly the length of
either na or (na + ns), whereas the current code only validates that the
property is at least that long. For non-failure cases, the two behaviours
are identical).

Cc: Przemyslaw Marczak <p.marczak@samsung.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Michal Suchanek <hramrach@gmail.com>
Fixes: 02464e386bb5 ("fdt: add new fdt address parsing functions")
Reported-by: Przemyslaw Marczak <p.marczak@samsung.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>