soc: ti: fix max dup length for kstrndup

If source string longer than max, kstrndup will alloc max+1 space.
So, we should make sure the result will not over limit.

Signed-off-by: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>