random: rand32_timer: Avoid alignment faults by using memcpy

The previous implementation assumed that the dst pointer was always
aligned to a 4-byte boundary in platforms that require alignment for
storage of 32-bit integers. Since this is required for certain platforms
(eg. Arm Cortex-M0), use memcpy() instead, which always takes
alignment into account.

Fixes #33969.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>