pwm: atmel-tcb: Make atmel_tcb_divisors static

The array atmel_tcb_divisors is not supposed to be used outside of the
driver, so make it static.

This fixes a sparse warning:

	drivers/pwm/pwm-atmel-tcb.c:64:10: warning: symbol 'atmel_tcb_divisors' was not declared. Should it be static?
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-atmel-tcb.c

@@ -61,7 +61,7 @@ struct atmel_tcb_pwm_chip {
 	struct atmel_tcb_channel bkup;
 };
 
-const u8 atmel_tcb_divisors[] = { 2, 8, 32, 128, 0, };
+static const u8 atmel_tcb_divisors[] = { 2, 8, 32, 128, 0, };
 
 static inline struct atmel_tcb_pwm_chip *to_tcb_chip(struct pwm_chip *chip)
 {