forked from Mirrors/opensbi

No need to compare characters when the count turns to 0. Fix the issue in sbi_strncmp. Signed-off-by: Dong Du <Dd_nirvana@sjtu.edu.cn> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> Reviewed-by: Anup Patel <anup.patel@wdc.com>