OMAPDSS: TFP410: use gpio_set_value_cansleep

The Beagleboard xM gpio used for TFP410 powerdown is connected through
an I2C attached chip which means setting the GPIO can sleep. Code that
calls tfp410_power_on/off holds a mutex, so sleeping should be fine.

Signed-off-by: Russ Dill <Russ.Dill@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>