lib/ext2fs: llseek: simplify linux section

lib/ext2fs: llseek: simplify linux section

On 32-bit musl systems, off_t is always 8 bytes regardless of
_FILE_OFFSET_BITS. The previous code did not cover this case.

The previous #ifdef logic was rather confusing, so I reworked it into a
more understandable form.

Bug: https://bugs.gentoo.org/908892
Signed-off-by: Mike Gilbert <floppym@gentoo.org>
Closes: https://github.com/tytso/e2fsprogs/pull/150
Signed-off-by: Sam James <sam@gentoo.org>
Link: https://lore.kernel.org/r/20231107233323.2013334-2-sam@gentoo.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>