User can get correct HCLK frequency during driver probe stage
by adding the following configuration in the device tree.
"clocks = <&scu ASPEED_CLK_AHB>".

Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>