knot: backport patch to fix linking with libhiredis

knot: backport patch to fix linking with libhiredis

It was discovered that even while using ``--enable-redis=no``
and ``--disable-redis`` that it was still linking with libhiredis.

This avoids to picking up libhiredis as dependency:

```
Package knot is missing dependencies for the following libraries:
libhiredis.so.1.1.0
```

Fixes: cbbd2b5b3bd6df7e550b114cf1c9f8e0f5bc8616 ("knot: disable redis as it was enabled since 3.5.0 by default")
Signed-off-by: Jan Hák <redacted>