mlxsw: spectrum_ptp: Fix compilation on 32-bit ARM

Compilation on 32-bit ARM fails after commit 992aa864 ("mlxsw:
spectrum_ptp: Add implementation for physical hardware clock operations")
because of 64-bit division:

arm-linux-gnueabi-ld:
drivers/net/ethernet/mellanox/mlxsw/spectrum_ptp.o: in function
`mlxsw_sp1_ptp_phc_settime': spectrum_ptp.c:(.text+0x39c): undefined
reference to `__aeabi_uldivmod'

Fix by using div_u64().

Fixes: 992aa864 ("mlxsw: spectrum_ptp: Add implementation for physical hardware clock operations")
Signed-off-by: Shalom Toledo <shalomt@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_ptp.c

@@ -81,13 +81,12 @@ static int
 mlxsw_sp1_ptp_phc_settime(struct mlxsw_sp_ptp_clock *clock, u64 nsec)
 {
 	struct mlxsw_core *mlxsw_core = clock->core;
+	u64 next_sec, next_sec_in_nsec, cycles;
 	char mtutc_pl[MLXSW_REG_MTUTC_LEN];
 	char mtpps_pl[MLXSW_REG_MTPPS_LEN];
-	u64 next_sec_in_nsec, cycles;
-	u32 next_sec;
 	int err;
 
-	next_sec = nsec / NSEC_PER_SEC + 1;
+	next_sec = div_u64(nsec, NSEC_PER_SEC) + 1;
 	next_sec_in_nsec = next_sec * NSEC_PER_SEC;
 
 	spin_lock(&clock->lock);