csky: bitops: Remove duplicate __clear_bit define

Building csky:allmodconfig results in the following build error.

In file included from ./include/linux/bitops.h:33,
                 from ./include/linux/log2.h:12,
                 from kernel/bounds.c:13:
./arch/csky/include/asm/bitops.h:77: error: "__clear_bit" redefined

Since commit 9248e52f ("locking/atomic: simplify non-atomic wrappers"),
__clear_bit is defined in include/asm-generic/bitops/non-atomic.h,
and the define in the csky include file is no longer necessary or useful.
Remove it.

Fixes: 9248e52f

 ("locking/atomic: simplify non-atomic wrappers")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guo Ren <guoren@kernel.org>