dt-bindings: clock: mediatek,mt7622-pciesys: Remove syscon compatible

dt-bindings: clock: mediatek,mt7622-pciesys: Remove syscon compatible

The PCIESYS register space contains a pure clock controller, which
has no system controller register, so this definitely doesn't need
any "syscon" compatible.

As a side note, luckily no devicetree ever added the syscon string
to PCIESYS clock controller node compatibles, so this also resolves
a dtbs_check warning for mt7622.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>