serial: pic32: Add checks for devm_clk_get() in pic32_uart_probe()

As the devm_clk_get() may return ERR_PTR, its return value needs to be
checked to avoid invalid poineter dereference.
Signed-off-by: Yuan Can <yuancan@huawei.com>
Link: https://lore.kernel.org/r/20221125093832.33386-1-yuancan@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/pic32_uart.c

@@ -889,6 +889,8 @@ static int pic32_uart_probe(struct platform_device *pdev)
 	sport->irq_rx		= irq_of_parse_and_map(np, 1);
 	sport->irq_tx		= irq_of_parse_and_map(np, 2);
 	sport->clk		= devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(sport->clk))
+		return PTR_ERR(sport->clk);
 	sport->dev		= &pdev->dev;
 
 	/* Hardware flow control: gpios