sh-pfc: Fix compiler warning when BUG()

The sh_pfc_phys_to_virt() function ends with a BUG() statement without a
return. When CONFIG_BUG isn't set the function will thus have no return
value. Fix it.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

drivers/pinctrl/sh-pfc/core.c

@@ -72,6 +72,7 @@ static void __iomem *sh_pfc_phys_to_virt(struct sh_pfc *pfc,
 	}
 
 	BUG();
+	return NULL;
 }
 
 int sh_pfc_get_pin_index(struct sh_pfc *pfc, unsigned int pin)