net: ll_temac: Make some functions static

Fix sparse warnings:

drivers/net/ethernet/xilinx/ll_temac_main.c:66:5: warning: symbol '_temac_ior_be' was not declared. Should it be static?
drivers/net/ethernet/xilinx/ll_temac_main.c:71:6: warning: symbol '_temac_iow_be' was not declared. Should it be static?
drivers/net/ethernet/xilinx/ll_temac_main.c:76:5: warning: symbol '_temac_ior_le' was not declared. Should it be static?
drivers/net/ethernet/xilinx/ll_temac_main.c:81:6: warning: symbol '_temac_iow_le' was not declared. Should it be static?
drivers/net/ethernet/xilinx/ll_temac_main.c:648:6: warning: symbol 'ptr_to_txbd' was not declared. Should it be static?
drivers/net/ethernet/xilinx/ll_temac_main.c:654:6: warning: symbol 'ptr_from_txbd' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>