overlays: Add updated mmc1 alias to sdio overlays

In the downstream RPi kernel, aliases are used to assign instance
numbers to the SD/MMC interfaces. The updated sdio overlays
effectively rename the device node, so the mmc1 alias has to be
updated in order to preserve the mmc1 numbering, otherwise the device
will appear as mmc2.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>