net: sch: api: fix tcf_block_get

The build of mips bcm47xx_defconfig is failing with the error:
net/sched/sch_fq_codel.c: In function 'fq_codel_init':
net/sched/sch_fq_codel.c:487:8: error:
	too many arguments to function 'tcf_block_get'

While adding the extack support, the commit missed adding it in the
headers when CONFIG_NET_CLS is not defined.

Fixes: 8d1a77f9 ("net: sch: api: add extack support in tcf_block_get")
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>