boards: st: dts: fix slot0_partition address error

The B_L4S5I_IOT01A Discovery kit does not boot up when using --sysbuild.
The error is caused by slot0_partition which is assigned an address of
0x1000 which overlaps with the boot_partition. Setting the address to
0x10000 fixed it.

Signed-off-by: Winston Arrocena <we.arrocena@gmail.com>