dt-bindings: arm: Trivial typo fixes in cpu-capacity.txt

Correct the spelling of 'cluster1@max-freq' and fix the wrong
capacity-dmips-mhz value 576 (which should be 578 instead).

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220208070300.1610-1-yuzenghui@huawei.com