package/fluidsynth: bump to version 2.2.0

package/fluidsynth: bump to version 2.2.0

For change log since v2.1.5, see:
- https://github.com/FluidSynth/fluidsynth/releases/tag/v2.1.6
- https://github.com/FluidSynth/fluidsynth/releases/tag/v2.1.7
- https://github.com/FluidSynth/fluidsynth/releases/tag/v2.1.8
- https://github.com/FluidSynth/fluidsynth/releases/tag/v2.2.0

./utils/test-pkg --package fluidsynth
6 builds, 2 skipped, 0 build failed, 0 legal-info failed

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>