erofs-utils: avoid silent corruption caused by `c_root_xattr_isize`

erofs-utils: avoid silent corruption caused by `c_root_xattr_isize`

When `c_root_xattr_isize` is too large, `i_xattr_icount` will overflow,
resulting in silent corruption of the filesystem image. This patch performs
checks in advance and reports errors.

Fixes: 8f93c2f83962 ("erofs-utils: mkfs: support inline xattr reservation for rootdirs")
Signed-off-by: Hongzhen Luo <hongzhen@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241127092825.4105724-1-hongzhen@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>