load_elf: fix iterator's type for elf file processing

load_elf: fix iterator's type for elf file processing

j is used while loading an ELF file to byteswap segments'
data. If data is larger than 2GB an overflow may happen.
So j should be elf_word.

This commit fixes a minor bug: it's unlikely anybody is trying to
load ELF files with 2GB+ segments for wrong-endianness targets,
but if they did, it wouldn't work correctly.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Cc: qemu-stable@nongnu.org
Fixes: 7ef295ea5b ("loader: Add data swap option to load-elf")
Signed-off-by: Anastasia Belova <abelova@astralinux.ru>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>