soxr: Update CMakeLists.txt with cmake min version

soxr: Update CMakeLists.txt with cmake min version

- The last update and commit on this package was 7 years ago so unlikely that there will
   be an update for this.
- An issue has been raised on the github site but as none of the other raised issues
   have been dealt with in the last 7 years it looks like this repo is dead.
- Will raise a separate discussion on whether this package should be left in IPFire.
- Patch created to update the min cmake version to 3.10 and the build completed
   successfully with that.

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>