can: mcp251xfd: mcp251xfd_probe(): try to get crystal clock rate from property

In some configurations, mainly ACPI-based, the clock frequency of the
device is supplied by very well established 'clock-frequency'
property. Hence, try to get it from the property at last if no other
providers are available.

Link: https://lore.kernel.org/r/20210531084444.1785397-1-mkl@pengutronix.deSigned-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -2860,7 +2860,7 @@ static int mcp251xfd_probe(struct spi_device *spi)
 	struct gpio_desc *rx_int;
 	struct regulator *reg_vdd, *reg_xceiver;
 	struct clk *clk;
-	u32 freq;
+	u32 freq = 0;
 	int err;
 
 	if (!spi->irq)
@@ -2887,11 +2887,19 @@ static int mcp251xfd_probe(struct spi_device *spi)
 		return dev_err_probe(&spi->dev, PTR_ERR(reg_xceiver),
 				     "Failed to get Transceiver regulator!\n");
 
-	clk = devm_clk_get(&spi->dev, NULL);
+	clk = devm_clk_get_optional(&spi->dev, NULL);
 	if (IS_ERR(clk))
 		return dev_err_probe(&spi->dev, PTR_ERR(clk),
 				     "Failed to get Oscillator (clock)!\n");
+	if (clk) {
 		freq = clk_get_rate(clk);
+	} else {
+		err = device_property_read_u32(&spi->dev, "clock-frequency",
+					       &freq);
+		if (err)
+			return dev_err_probe(&spi->dev, err,
+					     "Failed to get clock-frequency!\n");
+	}
 
 	/* Sanity check */
 	if (freq < MCP251XFD_SYSCLOCK_HZ_MIN ||