clk: sunxi-ng: a523: Mark MBUS clock as critical

The MBUS serves as the main data bus for various DMA masters in the
system. If its clock is not enabled, the DMA operations will stall,
leading to the peripherals stalling or timing out. This has been
observed as USB or MMC hosts timing out waiting for transactions
when the clock is automatically disabled by the CCF due to it not
being used.

Mark the clock as critical so that it never gets disabled.

Fixes: 74b0443a0d0a ("clk: sunxi-ng: a523: add system mod clocks")
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Link: https://patch.msgid.link/20250607135029.2085140-1-wens@kernel.org
Signed-off-by: Chen-Yu Tsai <wens@csie.org>