dracut-install: simplify ldd parsing logic

dracut-install: simplify ldd parsing logic

The previous logic would not handle absolute paths on the left side of
the "=>" properly. For example, on Gentoo ARM64, ldd outputs this:

	/lib/ld-linux-aarch64.so.1 => /lib64/ld-linux-aarch64.so.1

At runtime, the kernel tries to load the file from /lib, and fails if we
only provide it in /lib64.

Instead of looking for the first slash after the "=>", just look for the
first slash, period. This would fail if we somehow had a relative path
on the left side (foo/libbar.so), but I'm not aware of any binaries that
would contain such an entry in DT_NEEDED.

Bug: https://bugs.gentoo.org/667752
Signed-off-by: Mike Gilbert <floppym@gentoo.org>