erofs-utils: lib: fix reads for chunk-based files

Use erofs_io_read() to handle chunk read errors and short reads while
retrying EINTR without corrupting the buffer position.

Assisted-by: Codex:gpt-6-astra
Signed-off-by: Yifan Zhao <stopire@gmail.com>
Link: https://patch.msgid.link/20261013083517.2435363-1-stopire@gmail.com
Signed-off-by: Gao Xiang <xiang@kernel.org>