clk: sunxi-ng: sun50i: h6: Fix MMC clock mux width

MUX bits for MMC clock register range are 25:24 where 24 is shift
and 2 is width So fix the width number from 3 to 2.

Fixes: 524353ea ("clk: sunxi-ng: add support for the Allwinner H6 CCU")
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>