net/smc: remove unused inline function smc_curs_read

commit bac6de7b ("net/smc: eliminate cursor read and write calls")
left behind this.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>