cpu-exec: Also reload CPUClass *cc after longjmp return in cpu_exec()

Local variable CPUClass *cc needs to be reloaded after return from longjmp,
too.  (This fixes a mips-softmmu crash observed on FreeBSD when qemu is
built with clang.)

Reported-by: Dimitry Andric <dim@FreeBSD.org>
Signed-off-by: Juergen Lock <nox@jelal.kn-bremen.de>
Signed-off-by: Andreas Färber <afaerber@suse.de>