csky: mm: abort uaccess retries upon fatal signal

Pick up the patch from the 'Link' made by Mark Rutland. Keep the
same with x86, arm, arm64, arc, sh, power.

Link: https://lore.kernel.org/linux-arm-kernel/1499782763-31418-1-git-send-email-mark.rutland@arm.com/


Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Mark Rutland <mark.rutland@arm.com>