signal/nds32: Use force_sig(SIGILL) in do_revisn

As originally committed do_revisn would deliver a siginfo for SIGILL
with an si_code composed of random stack contents.  That makes no
sense and is not something userspace can depend on.  So simplify
the code and just use "force_sig(SIG_ILL, current)" instead.

Fixes: 2923f5ea ("nds32: Exception handling")
Cc: Vincent Chen <vincentc@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>