pwm: pca9685: clarify pca9685_set_sleep_mode() interface.

The function
static void pca9685_set_sleep_mode(struct pca9685 *pca, int sleep)
takes the chip in and out of sleep mode, depending on the value of
sleep, which is interpreted as a boolean.

To clarify that 'int sleep' is a boolean and not a sleep delay,
change the function interface to:
static void pca9685_set_sleep_mode(struct pca9685 *pca, bool enable)

Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>