clk: sunxi-ng: v3s: add missing clock slices for MMC2 module clocks

The MMC2 clock slices are currently not defined in V3s CCU driver, which
makes MMC2 not working.

Fix this issue.

Fixes: d0f11d14 ("clk: sunxi-ng: add support for V3s CCU")
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>