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/tavorevb.c

@@ -175,6 +175,7 @@ static struct platform_pwm_backlight_data tavorevb_backlight_data[] = {
 		.max_brightness	= 100,
 		.dft_brightness	= 100,
 		.pwm_period_ns	= 100000,
+		.enable_gpio	= -1,
 	},
 	[1] = {
 		/* secondary backlight */
@@ -182,6 +183,7 @@ static struct platform_pwm_backlight_data tavorevb_backlight_data[] = {
 		.max_brightness	= 100,
 		.dft_brightness	= 100,
 		.pwm_period_ns	= 100000,
+		.enable_gpio	= -1,
 	},
 };