cx231xx: fix compiler warnings

If CONFIG_VIDEO_CX231XX_RC is undefined, then these compiler warnings are generated:

In file included from drivers/media/usb/cx231xx/cx231xx-cards.c:23:0:
drivers/media/usb/cx231xx/cx231xx-cards.c: In function ‘cx231xx_release_resources’:
drivers/media/usb/cx231xx/cx231xx.h:982:30: warning: statement with no effect [-Wunused-value]

 #define cx231xx_ir_exit(dev) (0)
                              ^

drivers/media/usb/cx231xx/cx231xx-cards.c:1158:2: note: in expansion of macro ‘cx231xx_ir_exit’
cx231xx_ir_exit(dev);
^
drivers/media/usb/cx231xx/cx231xx-cards.c: In function ‘cx231xx_init_dev’:
drivers/media/usb/cx231xx/cx231xx.h:981:30: warning: statement with no effect [-Wunused-value]

 #define cx231xx_ir_init(dev) (0)
                              ^

drivers/media/usb/cx231xx/cx231xx-cards.c:1351:2: note: in expansion of macro ‘cx231xx_ir_init’
cx231xx_ir_init(dev);
^
drivers/media/usb/cx231xx/cx231xx-cards.c: In function ‘cx231xx_usb_probe’:
drivers/media/usb/cx231xx/cx231xx.h:982:30: warning: statement with no effect [-Wunused-value]

 #define cx231xx_ir_exit(dev) (0)
                              ^

drivers/media/usb/cx231xx/cx231xx-cards.c:1705:2: note: in expansion of macro ‘cx231xx_ir_exit’
cx231xx_ir_exit(dev);
^
drivers/media/usb/cx231xx/cx231xx-cards.c: In function ‘cx231xx_usb_disconnect’:
drivers/media/usb/cx231xx/cx231xx.h:982:30: warning: statement with no effect [-Wunused-value]

 #define cx231xx_ir_exit(dev) (0)
                              ^

drivers/media/usb/cx231xx/cx231xx-cards.c:1754:3: note: in expansion of macro ‘cx231xx_ir_exit’
cx231xx_ir_exit(dev);
^

Fix by using static inlines instead of defines.

index 573b3c0..9871c79f 100644
@@ -978,8 +978,11 @@ extern void cx231xx_417_unregister(struct cx231xx *dev);
 int cx231xx_ir_init(struct cx231xx *dev);
 void cx231xx_ir_exit(struct cx231xx *dev);
 #else
-#define cx231xx_ir_init(dev)	(0)
-#define cx231xx_ir_exit(dev)	(0)
+static inline int cx231xx_ir_init(struct cx231xx *dev)
+{
+	return 0;
+}
+static inline void cx231xx_ir_exit(struct cx231xx *dev) {}
 #endif
 
 static inline unsigned int norm_maxw(struct cx231xx *dev)