soc: sunxi: sram: Only iterate over SRAM children

Now that a regulators child is accepted by the controller binding, the
debugfs show routine must be explicitly limited to mmio-sram children.

Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20221208084127.17443-5-samuel@sholland.org


Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>