pinctrl: pinmux: Use seq_putc() in pinmux_pins_show()

A single character (line break) should be put into a sequence.
Thus use the corresponding function "seq_putc".

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinmux.c

@@ -617,7 +617,7 @@ static int pinmux_pins_show(struct seq_file *s, void *what)
 				   pctlops->get_group_name(pctldev,
 					desc->mux_setting->group));
 		else
-			seq_printf(s, "\n");
+			seq_putc(s, '\n');
 	}
 
 	mutex_unlock(&pctldev->mutex);