erofs: fix potential return value overflow of z_erofs_shrink_scan()

erofs: fix potential return value overflow of z_erofs_shrink_scan()

[ Upstream commit db902986dee453bfb5835cbc8efa67154ab34caf ]

z_erofs_shrink_scan() could return small numbers due to the mistyped
`freed`.

Although I don't think it has any visible impact.

Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250114040058.459981-1-hsiangkao@linux.alibaba.com
Signed-off-by: Sasha Levin <sashal@kernel.org>