csky: fix csky_cmpxchg_fixup not working

csky: fix csky_cmpxchg_fixup not working

[ Upstream commit 809ef03d6d21d5fea016bbf6babeec462e37e68c ]

In the csky_cmpxchg_fixup function, it is incorrect to use the global
variable csky_cmpxchg_stw to determine the address where the exception
occurred.The global variable csky_cmpxchg_stw stores the opcode at the
time of the exception, while &csky_cmpxchg_stw shows the address where
the exception occurred.

Signed-off-by: Yang Li <yang.li85200@gmail.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>