net: phy: dp83867: fix get nvmem cell fail

If CONFIG_NVMEM is not set of_nvmem_cell_get, of_nvmem_device_get
functions will return ERR_PTR(-EOPNOTSUPP) and "failed to get nvmem
cell io_impedance_ctrl" error would be reported despite "io_impedance_ctrl"
is completely missing in Device Tree and we should use default values.

Check -EOPNOTSUPP togather with -ENOENT to avoid this situation.

Fixes: 5c2d0a6 ("net: phy: dp83867: implement support for io_impedance_ctrl nvmem cell")
Signed-off-by: Nikita Shubin <n.shubin@yadro.com>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220805084843.24542-1-nikita.shubin@maquefel.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/dp83867.c

@@ -535,7 +535,7 @@ static int dp83867_of_init_io_impedance(struct phy_device *phydev)
 	cell = of_nvmem_cell_get(of_node, "io_impedance_ctrl");
 	if (IS_ERR(cell)) {
 		ret = PTR_ERR(cell);
-		if (ret != -ENOENT)
+		if (ret != -ENOENT && ret != -EOPNOTSUPP)
 			return phydev_err_probe(phydev, ret,
 						"failed to get nvmem cell io_impedance_ctrl\n");