sw64: fix sw64_set_rate()

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I56OLG



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This void method has no return value.

Signed-off-by: He Chuyue <hechuyue@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>