ARM: pxa: Initialize PWM backlight enable_gpio field

The GPIO API defines 0 as being a valid GPIO number, so this field needs
to be initialized explicitly.

A special case is the Palm Tungsten|C board. Since it doesn't use any
quirks that would require the existing .init() or .exit() hooks it can
simply use the new enable_gpio field.

Signed-off-by: Thierry Reding <treding@nvidia.com>

arch/arm/mach-pxa/raumfeld.c

@@ -539,6 +539,7 @@ static struct platform_pwm_backlight_data raumfeld_pwm_backlight_data = {
 	.dft_brightness	= 100,
 	/* 10000 ns = 10 ms ^= 100 kHz */
 	.pwm_period_ns	= 10000,
+	.enable_gpio	= -1,
 };
 
 static struct platform_device raumfeld_pwm_backlight_device = {