net: stmmac: Use mutex instead of spinlock

Some drivers, such as DWC EQOS on Tegra, need to perform operations that
can sleep under this lock (clk_set_rate() in tegra_eqos_fix_speed()) for
proper operation. Since there is no need for this lock to be a spinlock,
convert it to a mutex instead.

Fixes: e6ea2d16fc61 ("net: stmmac: dwc-qos: Add Tegra186 support")
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Tested-by: Bhadram Varka <vbhadram@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
index 4d425b1..fbfe5dc 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
@@ -122,7 +122,7 @@ struct stmmac_priv {
 	struct net_device *dev;
 	struct device *device;
 	struct mac_device_info *hw;
-	spinlock_t lock;
+	struct mutex lock;
 
 	/* RX Queue */
 	struct stmmac_rx_queue rx_queue[MTL_MAX_RX_QUEUES];