avr32/lib: fix unaligned memcpy()

memcpy(p, unaligned, 4..) returns (p + num_of_unaligned_by_copied)
instead of p because p is not preserved in the unaligned case.

Noticed by Herbert Xu's superior parameter recycling coding technique
which let the md4 self-test fail on avr32.

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>