Fix loop over ELF program header

`for (i = 0; i <= ehdr->e_phnum; i++) {` makes e_phnum + 1 iterations,
not e_phnum times. This has caused issue for reading bootloaders in ELF
format such as in FreeBSD:
https://cgit.freebsd.org/src/commit/?id=424089a0fc82ee9db8659b8c1099bbbde8999473.

Fix by replacing <= with <, so i iterates e_phnum times as expected.

Signed-off-by: Minsoo Choo <minsoo@minsoo.io>
Message-ID: <20260520220212.525-2-minsoo@minsoo.io>
Signed-off-by: Thomas Huth <th.huth@posteo.eu>