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>
diff --git a/arch/arm/mach-pxa/viper.c b/arch/arm/mach-pxa/viper.c
index 9c363c0..29905b1 100644
--- a/arch/arm/mach-pxa/viper.c
+++ b/arch/arm/mach-pxa/viper.c
@@ -401,6 +401,7 @@
 	.max_brightness	= 100,
 	.dft_brightness	= 100,
 	.pwm_period_ns	= 1000000,
+	.enable_gpio	= -1,
 	.init		= viper_backlight_init,
 	.notify		= viper_backlight_notify,
 	.exit		= viper_backlight_exit,