clk: sunxi-ng: d1: Add missing divider for MMC mod clocks

clk: sunxi-ng: d1: Add missing divider for MMC mod clocks

The D1/R528/T113 SoCs have a hidden divider of 2 in the MMC mod clocks,
just as other recent SoCs. So far we did not describe that, which led
to the resulting MMC clock rate to be only half of its intended value.

Use a macro that allows to describe a fixed post-divider, to compensate
for that divisor.

This brings the MMC performance on those SoCs to its expected level,
so about 23 MB/s for SD cards, instead of the 11 MB/s measured so far.

Fixes: 35b97bb94111 ("clk: sunxi-ng: Add support for the D1 SoC clocks")
Reported-by: Kuba Szczodrzyński <kuba@szczodrzynski.pl>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Link: https://patch.msgid.link/20250501120631.837186-1-andre.przywara@arm.com
Signed-off-by: Chen-Yu Tsai <wens@csie.org>