pinctrl: pinctrl-single: fix compile warning when no CONFIG_PM

This warning has been introduced by the commit
0f9bc4bcdf4f pinctrl: single: adopt pinctrl sleep mode management

Signed-off-by: Jean-Francois Moine <[e-mail]>
Acked-by: Tony Lindgren <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/pinctrl/pinctrl-single.c

···
 	return ret;
 }
 
+#ifdef CONFIG_PM
 static int pinctrl_single_suspend(struct platform_device *pdev,
 					pm_message_t state)
 {
···
 
 	return pinctrl_force_default(pcs->pctl);
 }
+#endif
 
 static int pcs_probe(struct platform_device *pdev)
 {