pinctrl: Combine substrings for a message in pin_config_group_get()

The script "checkpatch.pl" pointed information out like the following.

WARNING: quoted string split across lines

Thus fix the affected source code place.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinconf.c

@@ -87,9 +87,8 @@ int pin_config_group_get(const char *dev_name, const char *pin_group,
 	ops = pctldev->desc->confops;
 
 	if (!ops || !ops->pin_config_group_get) {
-		dev_dbg(pctldev->dev, "cannot get configuration for pin "
-			"group, missing group config get function in "
-			"driver\n");
+		dev_dbg(pctldev->dev,
+			"cannot get configuration for pin group, missing group config get function in driver\n");
 		ret = -ENOTSUPP;
 		goto unlock;
 	}