csky: Fix a size determination in gpr_get()

"*" is missed  in size determination as we are passing register set
rather than a pointer.

Fixes: dcad7854 ("sky: switch to ->regset_get()")
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>