ast2600: spl: Use readl for reading mmio

u-boot was crashing in qemu as the modeled hardware enforced overly
strict memory reads.

While this code will work on existing hardware, fix to avoid future issues.

Fixes: 12770d0df0e8 ("ast2600: spl: Add boot mode detection")
Link: https://gitlab.com/qemu-project/qemu/-/issues/2636
Signed-off-by: Joel Stanley <joel@jms.id.au>
1 file changed