target/arm: fix TCG leak for fcvt half->double

When support for the AHP flag was added we inexplicably only freed the
new temps in one of the two legs. Move those tcg_temp_free to the same
level as the allocation to fix that leak.

Fixes: 486624fc
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200131153439.26027-1-alex.bennee@linaro.org
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>