enetc: make enetc_setup_tc_mqprio static

While using ARCH=mips CROSS_COMPILE=mips-linux-gnu- command to compile,
make C=2 drivers/net/ethernet/freescale/enetc/enetc.o

one warning can be found:
drivers/net/ethernet/freescale/enetc/enetc.c:1439:5:
warning: symbol 'enetc_setup_tc_mqprio' was not declared.
Should it be static?

This patch make symbol enetc_setup_tc_mqprio static.
Fixes: 34c6adf1

 ("enetc: Configure the Time-Aware Scheduler via tc-taprio offload")
Signed-off-by: Mao Wenan <maowenan@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>