net: aquantia: Make function hw_atl_utils_mpi_set_speed() static

Fixes the following sparse warning:

drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_utils.c:508:5: warning:
 symbol 'hw_atl_utils_mpi_set_speed' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_utils.c

@@ -505,7 +505,7 @@ void hw_atl_utils_mpi_read_stats(struct aq_hw_s *self,
 err_exit:;
 }
 
-int hw_atl_utils_mpi_set_speed(struct aq_hw_s *self, u32 speed)
+static int hw_atl_utils_mpi_set_speed(struct aq_hw_s *self, u32 speed)
 {
 	u32 val = aq_hw_read_reg(self, HW_ATL_MPI_CONTROL_ADR);