dev: Avoid invalid sized reads in PL390 with DPRINTF enabled
dev: Avoid invalid sized reads in PL390 with DPRINTF enabled

The first DPRINTF() in PL390::writeDistributor always read a uint32_t, though a
packet may have only been 1 or 2 bytes.  This caused an assertion in
packet->get().
(transplanted from 72890a571a7bf9f8a416a1f4b15691667f69ec79)

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