leds: add help info about BCM63138 module name

It's what we do for all other LEDs drivers.
Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

drivers/leds/blink/Kconfig

@@ -10,6 +10,8 @@ config LEDS_BCM63138
 	  BCM63138 SoC. The same hardware block is known to be also used
 	  in BCM4908, BCM6848, BCM6858, BCM63148, BCM63381 and BCM68360.
 
+	  If compiled as module it will be called leds-bcm63138.
+
 config LEDS_LGM
        tristate "LED support for LGM SoC series"
        depends on X86 || COMPILE_TEST