misc: rtsx: Fix clock timing for RTS5261

This patch fix clock timing for RTS5261, using 256 divide
for the version higher than version C.

Signed-off-by: Rui Feng <rui_feng@realsil.com.cn>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/1604397321-3026-1-git-send-email-rui_feng@realsil.com.cn
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>