target/hppa: fix overwriting source reg in addb

target/hppa: fix overwriting source reg in addb

When one of the source registers is the same as the destination register,
the source register gets overwritten with the destionation value before
do_add_sv() is called, which leads to unexpection condition matches.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Message-Id: <20190311191602.25796-2-svens@stackframe.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>