csky: Correct position of _stext

Correct position of _stext to prevent check_kernel_text_object
warning [1].

[1] https://lore.kernel.org/linux-csky/YfLpNkmlvoR8iPcq@ls3530/



Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Helge Deller <deller@gmx.de>