sim: bfin: always do 16bit sign extension with the SEARCH insn

sim: bfin: always do 16bit sign extension with the SEARCH insn

The Blackfin PRM does not cover this case, but the hardware is clear: even
if the search criteria is not met (and thus a new 16bit value is loaded up
into the accumulator), the accumulator undergoes 16bit sign extension.  So
simply reload the low signed 16bits in that case.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>