leds: trigger: ledtrig-cpu:: Fix 'output may be truncated' issue for 'cpu'

In order to teach the compiler that 'trig->name' will never be truncated,
we need to tell it that 'cpu' is not negative.

When building with W=1, this fixes the following warnings:

  drivers/leds/trigger/ledtrig-cpu.c: In function ‘ledtrig_cpu_init’:
  drivers/leds/trigger/ledtrig-cpu.c:155:56: error: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 5 [-Werror=format-truncation=]
    155 |                 snprintf(trig->name, MAX_NAME_LEN, "cpu%d", cpu);
        |                                                        ^~
  drivers/leds/trigger/ledtrig-cpu.c:155:52: note: directive argument in the range [-2147483648, 7]
    155 |                 snprintf(trig->name, MAX_NAME_LEN, "cpu%d", cpu);
        |                                                    ^~~~~~~
  drivers/leds/trigger/ledtrig-cpu.c:155:17: note: ‘snprintf’ output between 5 and 15 bytes into a destination of size 8
    155 |                 snprintf(trig->name, MAX_NAME_LEN, "cpu%d", cpu);
        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 8f88731d ("led-triggers: create a trigger for CPU activity")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/3f4be7a99933cf8566e630da54f6ab913caac432.1695453322.git.christophe.jaillet@wanadoo.frSigned-off-by: Lee Jones <lee@kernel.org>

drivers/leds/trigger/ledtrig-cpu.c

@@ -130,7 +130,7 @@ static int ledtrig_prepare_down_cpu(unsigned int cpu)
 
 static int __init ledtrig_cpu_init(void)
 {
-	int cpu;
+	unsigned int cpu;
 	int ret;
 
 	/* Supports up to 9999 cpu cores */
@@ -152,7 +152,7 @@ static int __init ledtrig_cpu_init(void)
 		if (cpu >= 8)
 			continue;
 
-		snprintf(trig->name, MAX_NAME_LEN, "cpu%d", cpu);
+		snprintf(trig->name, MAX_NAME_LEN, "cpu%u", cpu);
 
 		led_trigger_register_simple(trig->name, &trig->_trig);
 	}