phy: starfive: remove unused struct 'regval'

'regval' is unused since the original
commit f8aa6608 ("phy: starfive: Add mipi dphy rx support").

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Changhuang Liang <changhuang.liang@starfivetech.com>
Link: https://lore.kernel.org/r/20240527205937.165325-1-linux@treblig.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>