arch/csky: fix some Kconfig typos

Fix wording in help text for the CPU_HAS_LDSTEX symbol.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>