textsearch: convert kmalloc + memset to kzalloc

convert kmalloc + memset to kzalloc for alloc_ts_config

Signed-off-by: Joonwoo Park <joonwpark81@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>