linux-user: Fixed cpu restore with pc 0 on SIGBUS

linux-user: Fixed cpu restore with pc 0 on SIGBUS

Commit f4e1168198 (linux-user: Split out host_sig{segv,bus}_handler)
introduced a bug, when returning from host_sigbus_handler the PC is
never set. Thus cpu_loop_exit_restore is called with a zero PC and
we immediate get a SIGSEGV.

Signed-off-by: Robbin Ehn <rehn@rivosinc.com>
Fixes: f4e1168198 ("linux-user: Split out host_sig{segv,bus}_handler")
Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Message-Id: <33f27425878fb529b9e39ef22c303f6e0d90525f.camel@rivosinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit 6d913158b5023ac948b8fd649d77fc86e28072f6)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>