leds: Make default trigger fields const

The default_trigger fields of struct gpio_led and thus struct
led_classdev are pretty much always assigned from a string literal,
which means the string can't be modified.  Which is fine, since there is
no reason to modify the string and in fact it never is.

But they should be marked const to prevent such code from being added,
to prevent warnings if -Wwrite-strings is used, when assigned from a
constant string other than a string literal (which produces a warning
under current kernel compiler flags), and for general good coding
practices.
Signed-off-by: Trent Piepho <tpiepho@freescale.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

include/linux/leds.h

@@ -123,7 +123,7 @@ extern void ledtrig_ide_activity(void);
  */
 struct led_info {
 	const char	*name;
-	char		*default_trigger;
+	const char	*default_trigger;
 	int		flags;
 };
 
@@ -135,7 +135,7 @@ struct led_platform_data {
 /* For the leds-gpio driver */
 struct gpio_led {
 	const char *name;
-	char *default_trigger;
+	const char *default_trigger;
 	unsigned 	gpio;
 	u8 		active_low;
 };