serial: sprd: check for NULL after calling devm_clk_get

In platforms which does not use CLK framework (HAVE_CLK not set), the
clk_* functions return NULL instead of an error. This patch handles that
scenario.

Signed-off-by: Fernando Guzman Lugo <[e-mail]>
Signed-off-by: Chunyan Zhang <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/sprd_serial.c

···
 	up->flags = UPF_BOOT_AUTOCONF;
 
 	clk = devm_clk_get(&pdev->dev, NULL);
-	if (!IS_ERR(clk))
+	if (!IS_ERR_OR_NULL(clk))
 		up->uartclk = clk_get_rate(clk);
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);